i
Dietary energy manipulations and
reproductive performance in primiparous sows
Tai Yuan Chen
Submitted for the Degree of Doctor of Philosophy
In the School of
Animal and Veterinary Sciences,
Faculty of Sciences,
University of Adelaide
December 2012
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Table of Contents
Abstract ......................................................................................................................... ix
Declaration ................................................................................................................... xii
Publication list ........................................................................................................... xiii
Contributions of jointly authored papers .................................................................... xiv
Acknowledgements ...................................................................................................... xv
Chapter 1 Literature review ....................................................................................... 2
1.1 Introduction .................................................................................................... 2
1.2 Physiological influences in lactation associated with reproductive
performance .............................................................................................................. 4
1.2.1 Feed intake deficiency in first litter lactating sows ................................ 4
1.2.2 Influence on lactation feed intake by metabolic hormones .................... 6
1.2.2.1 Leptin ............................................................................................... 6
1.2.2.2 Insulin .............................................................................................. 7
1.2.3 Effect of body reserves change on reproductive performance ................ 8
1.3 Mechanism of energy balance effects on reproductive performance ............. 9
1.3.1 Energy deficiency and reproductive performance interactions .............. 9
1.3.2... Follicle recruitment and development, ovulation rate and embryo survival
............................................................................................................................. 13
1.3.3 Pre- and post-weaning gonadotrophin changes and follicle
development…………………………………………………………………….14
1.3.3.1 Pre-weaning gonadotropic secretion ............................................. 14
1.3.3.2 Post-weaning gonadotropic secretion ............................................ 15
1.3.3.3 Nutrition and gonadotropins .......................................................... 16
1.3.3.4 Progesterone .................................................................................. 17
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1.3.4 Metabolic hormones and ovarian function ........................................... 18
1.3.4.1 Insulin, IGF-I and glucose ............................................................. 18
1.3.4.2 Leptin ............................................................................................. 20
1.4 Measures to counteract second litter syndrome ........................................... 21
1.4.1 Pre-weaning repair strategies ................................................................ 21
1.4.1.1 Protein (lysine) supply ................................................................... 21
1.4.1.2 Energy sources ............................................................................... 22
1.4.1.3 Reduced suckling ........................................................................... 23
1.4.2 Post-weaning repair strategies .............................................................. 25
1.4.2.1 Nutrition or insulin administration ................................................ 25
1.4.2.2 Skip-a-heat and altrenogest administration ................................... 26
1.5 Aim of this thesis.......................................................................................... 27
Chapter 2 Comparison of maternal body condition changes during lactation
and status at weaning on subsequent reproductive performance in
primiparous sows: on-farm survey
Chapter 2 ...................................................................................................................... 30
2.1 Introduction .................................................................................................. 30
2.2 Methods ........................................................................................................ 31
2.2.1 Animals, housing and feeding............................................................... 31
2.2.2 Measurements ....................................................................................... 31
2.2.3 Calculations and statistical analysis ...................................................... 32
2.2.3.1 Model 1- sow body weight changes during lactation .................... 33
2.2.3.2 Model 2 - Sow body weight at weaning ........................................ 33
2.3 Results .......................................................................................................... 34
2.3.1 Univarite effect of body weight change (model 1) ............................... 34
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2.3.2 Sow body weight change and body weight at weaning in a multivariate
model (model 2) .................................................................................................. 37
2.3.3 Litter growth during lactation and subsequent litters ........................... 39
2.3.4 Correlations ........................................................................................... 39
2.4 Discussion .................................................................................................... 42
Chapter 3 Undernutrition during early follicle development has irreversible
effects on ovulation rate and embryos
Chapter 3 ...................................................................................................................... 46
3.1 Introduction .................................................................................................. 46
3.2 Methods ........................................................................................................ 47
3.2.1 Experimental design.............................................................................. 47
3.2.2 Animals, housing and feeding............................................................... 47
3.2.3 Treatments............................................................................................. 48
3.2.4 Oestrus detection and insemination ...................................................... 49
3.2.5 Measurements and observations ........................................................... 50
3.2.6 Calculations and statistical analyses ..................................................... 53
3.3 Results .......................................................................................................... 54
3.4 Discussion .................................................................................................... 61
Chapter 4 Effects of pre-weaning substitutions on plasma insulin and glucose
profiles in primiparous sows
Chapter 4 ...................................................................................................................... 67
4.1 Introduction .................................................................................................. 67
4.2 Materials and Methods ................................................................................. 68
4.2.1 General experimental design ................................................................. 68
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4.2.2 Animals, housing and feeding............................................................... 68
4.2.3 Observation and blood sampling .......................................................... 70
4.2.4 Plasma analyses .................................................................................... 72
4.2.5 Calculations and statistical analyses ..................................................... 72
4.3 Results .......................................................................................................... 73
4.4 Discussion .................................................................................................... 75
Chapter 5 Effects of pre-weaning energy substitutions on post-weaning follicle
development, steroid hormones and subsequent litter size in
primiparous sows
Chapter 5 ...................................................................................................................... 80
5.1 Introduction .................................................................................................. 80
5.2 Materials and Methods ................................................................................. 82
5.2.1 General experimental design ................................................................. 82
5.2.2 Animals, housing and feeding............................................................... 82
5.2.3 Oestrus detection and insemination ...................................................... 85
5.2.4 Measurements and observations ........................................................... 87
5.2.5 Calculations and statistical analyses ..................................................... 89
5.3 Results .......................................................................................................... 89
5.3.1 Sow performance .................................................................................. 89
5.3.2 Follicular development and plasma steroid hormone concentrations ... 91
5.3.3 Litter size and birth weights for the second litter ................................. 93
5.4 Discussion .................................................................................................... 95
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Chapter 6 General discussion
Chapter 6 .................................................................................................................... 103
6.1 Introduction ................................................................................................ 103
6.2 Body reserves mobilisation during lactation and the status at weaning ..... 103
6.3 Influence of pre- and post-weaning energy balance on ovarian function and
reproductive performance ..................................................................................... 106
6.4 Potential improvement for reproductive performance in primiparous sows
…………………………………………………………………………….107
6.5 Practical and future research recommendations ......................................... 109
6.6 Conclusion .................................................................................................. 111
References ................................................................................................................. 113
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LIST OF TABLES
TABLE 1.1 BREEDING HERD PERFORMANCE IN AUSTRALIA ............................................ 3
TABLE 1.2 FEED LEVELS DURING LACTATION ON SUBSEQUENT REPRODUCTIVE
PERFORMANCE IN YOUNG SOWS ................................................................... 12
TABLE 2.1 REPRODUCTIVE PERFORMANCE BASE ON BODY WEIGHT LOSS DURING
LACTATION .................................................................................................. 36
TABLE 2.2 REPRODUCTIVE PERFORMANCE BASE ON SOW BODY WEIGHT AT WEANING 38
TABLE 2.3 LITTER PERFORMANCE DURING LACTATION BASE ON SOW BODY WEIGHT
LOSS ............................................................................................................ 40
TABLE 2.4 LITTER PERFORMANCE DURING LACTATION BASE ON SOW BODY WEIGHT AT
WEANING ..................................................................................................... 41
TABLE 3.1 COMPOSITION OF EXPERIMENT DIETS (AS FED BASIS) .................................. 50
TABLE 3.2 GILT BODY WEIGHT CHANGES AND REPRODUCTIVE TRAITS ........................ 56
TABLE 4.1COMPOSITION OF EXPERIMENT DIETS (AS FED BASIS) .................................. 71
TABLE 5.1 COMPOSITION OF EXPERIMENTAL DIETS (AS FED BASIS) ............................. 86
TABLE 5.2 SOW BODY WEIGHT CHANGES AND REPRODUCTIVE TRAITS DURING
LACTATION .................................................................................................. 91
TABLE 5.3 EFFECTS OF TREATMENTS ON SUBSEQUENT LITTER SIZE ............................. 94
TABLE 6.1 DIGESTIBLE ENERGY INTAKE DURING LACTATION IN FOUR TREATMENTS . 106
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LIST OF FIGURES FIGURE 3.1 FOLLICLE DIAMETER AS DETERMINED USING TRANSCUTANEOUS
ULTRASONOGRAPHY FROM (A) FIVE DAYS BEFORE LUTEOLYSIS (D 0) TO (B)
THE SUBSEQUENT OVULATION. HH AND LL WERE FED A HIGH (1 M + 1.5
KG) AND A LOW (1 M) FEED LEVEL DURING THE LUTEAL PHASE AND
FOLLICULAR PHASE. HL AND LH RECEIVED A HIGH AND A LOW FEED LEVEL
DURING THE LUTEAL PHASE AND DURING THE FOLLICULAR PHASE WERE
THEN SWITCHED TO A LOW, OR A HIGH FEED LEVEL. OVU = 6 H BEFORE
OVULATION. * P < 0.05, ** P < 0.005. ........................................................... 59 FIGURE 3.2 PLASMA OESTRADIOL CONCENTRATIONS FOR INDIVIDUAL GILTS ON DAY
3 AND DAY 4 AFTER LUTEOLYSIS (DAY 0) IN THE FOUR TREATMENTS. SOME
GILTS IN THE HL AND LL TREATMENTS HAD OESTRADIOL LEVELS BELOW
THE DETECTION LIMIT (4.5 PG/ML) ON DAY 3; THESE ARE (ARBITRARILY)
REPRESENTED AT 2 PG/ML. OESTRADIOL CONCENTRATIONS ON DAY 3
(INCLUDING CONCENTRATIONS < 4.5 PG/ML SAMPLES) WERE INFLUENCED
BY FEEDING LEVEL DURING THE FOLLICULAR PHASE (P < 0.05). THE TWO
GILTS ON DAY 4 WITH OESTRADIOL BELOW DETECTION LEVEL
(REPRESENTED AS 2 PG/ML) OTHERWISE HAD NORMAL OESTRUS, OVULATION, AND FERTILISATION. .................................................................. 60
FIGURE 3.3 PLASMA PROGESTERONE CONCENTRATIONS AT 30 H, 54 H, 78 H AND 102
H AFTER OVULATION (0 H) IN THE FOUR TREATMENTS. VALUES DIFFERED
BETWEEN LH AND LL (P < 0.05). .................................................................. 61 FIGURE 4.1 PLASMA GLUCOSE PROFILES FOR CONTROL (C, N = 7), FAT (F, N = 6)
AND SUGAR (S, N = 8) TREATMENTS DURING LATE LACTATION. ABCTIME
POINTS WITH DIFFERENT SUPERSCRIPTS/SUBSCRIPTS DIFFER SIGNIFICANTLY
(P < 0.05). ..................................................................................................... 74 FIGURE 4.2 PLASMA INSULIN PROFILES FOR CONTROL (C, N = 7), FAT (F, N = 6) AND
SUGAR (S, N = 8) TREATMENTS DURING LATE LACTATION. ABC TIME POINTS
WITH DIFFERENT SUPERSCRIPTS/SUBSCRIPTS DIFFER SIGNIFICANTLY (P <
0.05). ............................................................................................................. 75 FIGURE 5.1 FOLLICLE DIAMETER AS DETERMINED USING RECTAL
ULTRASONOGRAPHY FROM WEANING (DAY 0) OR ALTRENOGEST
WITHDRAWAL TO OVULATION. ....................................................................... 92 FIGURE 5.2 PLASMA PROGESTERONE CONCENTRATIONS AT DAY 2 AND DAY 4 AFTER
OVULATION (OVULATION = DAY 0) IN THE FOUR TREATMENTS. CONCENTRATION AT DAY 4 WAS SIGNIFICANTLY HIGHER IN S TREATMENT
(P < 0.05). ..................................................................................................... 93 FIGURE 5.3 SUBSEQUENT LITTER SIZE IS DIVIDED IN THREE CLASSES (NUMBER OF
TOTAL BORN <= 10, 11- 13 AND > 13) AND PRESENTED AS PERCENTAGE IN
THE FOUR TREATMENTS (P < 0.05). ............................................................... 95
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Abstract
In primiparous sows, feed intake is generally insufficient to meet lactation demands.
Inadequate nutrient supply increases mobilisation of body reserves and, as a
consequence, affects subsequent reproduction. Excessive loss of body reserves during
lactation is not only associated with delayed post-weaning oestrus and the size of the
subsequent litter, but also increases culling rate and reduces sow longevity and the
productivity of the breeding herd. The aim of the thesis was to develop a clear
understanding of the impact of a negative energy balance during lactation on the
reproductive performance of modern primiparous sows in Australia, and evaluate
feeding strategies involving energy manipulations during crucial periods intended to
improve subsequent litter size.
In the first study, the associations of sow body weight changes during lactation and
the body weight at weaning with subsequent reproductive performance were studied
to investigate breeding herd performance in South Australia. By minimising body
weight loss and maintain adequate body reserves at weaning through the supply of
sufficient energy when rearing equal to or less than ten piglets during lactation, the
post-weaning reproductive performance and fertility had no influence in modern
primiparous sows.
In the second study, the carry-over effects of energy intake during the early antral
phase and subsequent follicular phase on follicle recruitment and ovulation rate were
assessed using a gilt model. Follicle size at the end of the luteal phase was greater for
gilts that were previously fed at a high feed level. During the follicular phase, high
feeding increased follicle size at Day 5 and plasma oestradiol concentration.
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Nevertheless, a low feed level during the luteal phase reduced ovulation rate and the
number of embryos, and this was not counteracted by feed level during the follicular
phase. Plasma progesterone concentration after ovulation was lower for gilts that
were restricted-fed throughout the whole period than for other treatments. These
results indicate that undernutrition during early antral follicular development has a
residual effect on follicle recruitment and quality.
In the third study, the effects of substituting 1 kg of a standard lactation diet with 1 kg
of a sugar-rich or fat-rich diet during late lactation on blood glucose and insulin
changes were investigated. The results demonstrated that a sugar-enriched diet during
the last week of lactation elevates circulating glucose and insulin concentrations, and
offer a means to improve post-weaning fertility in primiparous sows. Therefore, the
fourth study investigated the effects of pre-weaning energy substitutions plus post-
weaning altrenogest treatment as positive control on follicular development,
endocrine characteristics and subsequent litter size in primiparous sows. The
weaning-to-ovulation interval tended to be reduced in the sugar-rich treatment,
although body weight loss during the treatment period, post-weaning follicle
development, plasma oestradiol and pre-weaning leptin did not differ among
treatments, except body weight loss was lower and leptin was higher in the
altrenogest treatment. Post-ovulatory progesterone concentration in the sugar
treatment was higher. Sows in the sugar-rich and altrenogest treatments had a greater
proportion of litters with larger litter sizes. The outcome indicates that increasing
circulating insulin and glucose concentrations during late lactation or a week of
metabolic recovery produces large subsequent litter size in primiparous sows.
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Industry will be able to achieve an improvement of reproductive performance by
maximising energy intake (using an insulin-stimulating diet) during late lactation, or
by post-weaning altrenogest administration for a week for energy restoration.
Otherwise, adverse impacts of a negative energy balance during lactation will be
carried over into the mating period, and will depress subsequent reproductive
performance.
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Declaration
I certify that this work contains no material which has been accepted for the award of
any other degree or diploma in any university or other tertiary institution and, to the
best of my knowledge and belief, contains no material previously published or
written by another person, except where due reference has been made in the text. In
addition, I certify that no part of this work will, in the future, be used in a submission
for any other degree or diploma in any university or other tertiary institution without
the prior approval of the University of Adelaide and where applicable, any partner
institution responsible for the join-award of this degree.
I give consent to this copy of my thesis when deposited in the University Library,
being made available for loan and photocopying, subject to the provisions of the
Copyright Act 1968.
The author acknowledges that copyright of published works contained within this
thesis (as listed below) resides with the copyright holder(s) of those works. I also give
permission for the digital version of my thesis to be made available on the web, via
the University's digital research repository, the Library catalogue and also through
web search engines, unless permission has been granted by the University to restrict
access for a period of time.
December 2012
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Publication list
Chapter 3: Undernutrition during early follicle development has irreversible effects
on ovulation rate and embryos
T.Y. ChenA, P. StottA, R.Z. AthornA, E.G. BouwmanB, and P. LangendijkB
ASchool of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy Campus, Roseworthy, South Australia, 5371. BSouth Australian Research and Development Institute, Roseworthy Campus, Roseworthy, South Australia, 5371.
Published in 2012 Journal of Reproduction, Fertility and Development (24) 886-892
Chapter 4: Effects of pre-weaning substitutions on plasma insulin and glucose
profiles in primiparous sows
T.Y. ChenAB, P. StottA, S. O’LearyC, R. Z. AthornA, E. G. BouwmanB and P. LangendijkAB
ASchool of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy Campus, Roseworthy, SA, Australia BSouth Australian Research and Development Institute, Roseworthy Campus, Roseworthy, SA, Australia CDiscipline of Obstetrics and Gynaecology, The University of Adelaide, Adelaide, SA, Australia Published in 2012 Journal of Animal Physiology and Animal Nutrition. DOI: 10.1111/j.1439-0396.2012.01321.x
Chapter 5: Effects of pre-weaning energy substitutions on post-weaning follicle
development, steroid hormones and subsequent litter size in primiparous sows
T.Y. ChenAB, P. StottA, E.G. BouwmanB and P. LangendijkB
ASchool of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy Campus, Roseworthy, South Australia, 5371. BSouth Australian Research and Development Institute, Roseworthy Campus, Roseworthy, South Australia, 5371.
Published in 2012. Reproduction in Domestic Animals. DOI:10.1111/rda.12118
xiv
Contributions of jointly authored papers
The work presented in the thesis was carried out in collaboration between all authors
in three publications that contains in the thesis. Dr Philip. Stott and Dr Pieter.
Langendijk provided sufficient supervision on project conception, research direction,
experiment design and data analysis throughout all experiments, and approved the
manuscripts. In particular, they made arrangements to cover the research funding
required for the studies. Dr Sean O’Leary performed non-surgical ear vein
catheterization to allow serial blood sample collection. Mrs Emmy Bouwman
provided a scanning training program using ultrasound device and taught essential
skills that were needed for measurements and sample collections at field and also in
the laboratory. Miss Rebecca Athorn assisted data collection during the experimental
period.
The (co)-authors give permission for the publications of their collaboration to be
included in the thesis.
Dr Philip Stott
Dr Pieter Langendijk
Dr Sean O’Leary
Emmy Bouwman
Rebecca Athorn
xv
Acknowledgements
I cannot remember how many times I looked at the dawn sunlight through my office
window when I was trying to write up my papers and thesis, and now, it is time to
close the book! During this four years study journey, I have been through lots of
difficult situations but fortunately there was always someone who would like to help
me out and make my study and life here much easier. To begin with, I would very
much like to thank my supervisors Dr Philip Stott and Dr Pieter Langendijk for their
high tolerance of my poor English communication skills and their help to make my
PhD degree possible, particularly with minimal research grant support. They were not
just simply my supervisors to guide me on research conception but also like friends
that gave me comfort and support from the beginning. In addition, I have never seen
such an incredible woman as Emmy Bouwman, who was able to chase pigs around
for projects during her entire pregnancy, and contributed an amazing amount of time
helping me out with training in study skills and data collection. Also, the staff at the
PPPI Roseworthy piggery, in particular, the manager Andre Opperman, and former
staff David McNeill and Chris Craven provided sufficient animals, facilities and
assistance throughout my experiments.
During my six years overseas, I would like to thank my family for all the moral
support and encouragement that I received. Dad, Mum and my brother, you are so
important to me in my life, and I knew I could not finish my study without your
support. My Greek host family and relatives, your generosity and kindness mean a lot
to a person who was a thousand miles away from home, and you always treated me as
one of the family members and offered me lots of food for many years to stave off
starvation. And of course, all my friends here, they always tried to cheer me up and
xvi
they never gave up on me, particularly those friends who helped me through the
difficult times or offered affordable accommodations during my first two years. In
short, I am so very grateful all the people who I mentioned above, if you had not been
there to stand by me I may have been gone by now. Finally, I would like to thank all
the security guards who came to check on me in the middle of the night, seven days a
week for these years, to make sure I was still alive in my office. I can tell you guys “I
finished my PhD and I am still breathing!”.
1
Chapter 1
Literature review
2
Chapter 1
1.1 Introduction
The pig industry has changed rapidly over the last decades from an extensive to an
intensive production system. With the change of system, reproductive performance has
become an important determinant of sow productivity, as measured by the number of
piglets born alive per parity (Serenius and Stalder, 2004) and/or the number of pigs
born alive over the lifetime of the sow (Lucia et al., 1999). The way to achieve a high
average reproductive score per year is to improve sow longevity, which increases the
proportion of multiparous sows in a breeding herd while sows approach their
maximum productivity. Also, improving longevity of sows reduces the costs of
replacement per year.
In the past ten years, there has been little improvement in breeding herd performance
in the Australian pig industry (Table 1.1), and approximately 54.8 % of sows are
replaced every year and have on average 2.3 litters/sow/year (Australian Pork Ltd,
2012). It is generally considered that the above average replacement rate largely
reflects reproductive failure problems and, as is the case worldwide, has mainly occurs
in young sows (Engblom et al., 2007; Lucia et al., 2000). Analyses of reasons for
culling show that reproductive failure is the major reason for the disposal of young
sows, accounting for about 42 % of first litter culls (Lucia et al., 2000). Apart from
that, these young sows have a lower farrowing rate or so called “second litter
syndrome”, with the number of piglets in the second litter similar to or lower than in
the first litter, and can be expected to have a low litter sizes in subsequent parities
(Hoving et al., 2011). Reproduction among breeding herds is a cumulative process and
depends on body condition and nutrient supply when physiological challenges occur in
3
the sows. The major cause of poor reproductive performance in the second parity
seems to be that most primiparous sows at their first parturition are physiologically
immature and their intake of nutrients is insufficient to support milk production during
their first lactation; particularly modern lean sows which demand higher energy and
nutrient intake than sows in the past decades (Yang et al., 2008).
Table 1.1 Breeding herd performance in Australia
Parameter 1997 2002 2007 2012
Sow replacement rate, % 72.3 64.8 35.06 54.8 No. total pigs born alive/Litter 11.1 11.5 11.5 11.5 No. pigs born alive/Litter 10.2 10.5 10.5 10.8 Pigs weaned/Litter 8.9 9.2 9.16 9.54 Litter/Sow/Year 2.22 2.17 2.26 2.27 Pig weaned/Sow/Year 19.6 19.7 20.73 21.8 Weaning-to-service, days 7.1 6.2 8.2 6.9
(Australian Pork Ltd, 1997; 2002; 2007; 2012)
Regulation of energy balance is crucial for lactating sows to maintain their body
demands and milk production. Prunier et al. (1993) and Thaker and Bilkei (2005)
reported that primiparous sows lose 10 to 15 % of body weight or more during
lactation, reducing their reproductive performance and fertility. Studies have also
confirmed that sufficient energy support during lactation could maximise post-weaning
reproductive performance (Koketsu et al., 1996a) and improve subsequent litter size
(Vinsky et al., 2006) in primiparous sows. Furthermore, energy intake during lactation
and sow metabolic state at weaning determine the post-weaning reproductive
performance via mediation of metabolic hormones and secretion of reproductive
hormones (Prunier and Quesnel, 2000b).
4
The primary intention of this review is to study the relationship between energy
balance (maternal body reserves), metabolites and endocrine changes, and also the
effects of their interaction on follicle development and ovarian function in primiparous
sows from the onset of their first lactation through the post-weaning ovulation. This
will provide from recent research possible physiological mechanisms that may be
affecting the reproductive axis in modern primiparous sows, and those mechanisms
were investigated in the experiments described subsequently.
1.2 Physiological influences in lactation associated with reproductive
performance
1.2.1 Feed intake deficiency in first litter lactating sows
Lactation feed intake by sows can be influenced by several factors, mainly genetic
selection and feeding regimes during gestation and sow appetite during lactation.
Modern pig genotypes have been selected for production traits. In our knowledge,
selection for production traits results in an increased feed conversion rate, increased
growth rate and a reduction of backfat for marketing, and as a consequence, a
decreased reserve of body fat mass could be indirectly caused by the selection for these
production traits (Eissen et al., 2000). Additionally, the restricted feeding program for
pregnant gilts in current use is only intended to meet their energy requirement during
gestation to avoid compromising feed intake during lactation (Boyd et al., 2000a;
Everts and Dekker, 1995; Revell et al., 1998). Moreover, recommended and practised
post-farrowing feeding patterns are to increase feed intake gradually during first week
of lactation to reduce refusals and avoid post-partum agalactia (Neil, 1996). Thus, a
negative energy balance may have been exacerbated during the first week of lactation
5
by step-up feeding. Further, a low appetite during lactation is generally believed to be
due to limitations of stomach capacity in primiparous sows compared to multiparous
sows (Noblet et al., 1990). Taken together, highly prolific primiparous sows may have
insufficient body reserves at farrowing and suffer severe loss of body reserves due to
negative energy balance that cause by the energy drain of milk production during
lactation (Clowes et al., 2003a; Eissen et al., 2003).
Primiparous lactating sows (about 200 kg after farrowing), need at least 21.1 MJ
DE/day for maintenance and 60.8 MJ DE/day for milk production to rear 10 piglets,
which is equal to 5.6 kg/day of feed (14.5 MJ DE/kg) during lactation (Close and Cole,
2000). Primiparous sows produce approximately 2 kg/day of milk one day after
farrowing, increasing to 8.5 kg/day during the last (4th) week of lactation (Beyer et al.,
2007; Pluske et al., 1998; Revell et al., 1998b). The average milk yield for a sow
depends on many factors, but for first litter sows it is known to be influenced mainly
by litter size, body weight at farrowing and nutrition received. Previous studies by
Revell et al. (1998b) and Beyer et al. (2007) indicated that sows with greater lean
reserves produce more milk after farrowing or throughout lactation than sows with
greater fat reserves, suggesting that sows mobilise their body protein reserve to support
the demands of milk production when they are fed below their energy requirement in
the beginning of lactation (Yung et al., 2009), but become more dependent on feed
intake level as body weight is progressively lost through the lactation (Mullan and
Williams, 1989). In addition, milk yield increases in response to the stimulatory effect
of large litter sizes (Kim and Easter, 2001).
6
Therefore, increasing feed intake during gestation to achieve a heavier body weight at
farrowing has been suggested as a solution, enabling sows to increase body reserves in
anticipation of lactational energy demands. However, sows that were fed a high feed
level during gestation have compromised feed intake during lactation, and mobilise
more body fat and protein reserves to overcome the energy demands of lactation
(Dourmad, 1991; Prunier et al., 2001; Quesnel et al., 2005a; Revell et al., 1998). Apart
from that, a higher energy demand for maintenance in heavier lactating sows has been
found by Young et al. (2005), and a reduction of appetite is associated with post-
farrowing circulating leptin and insulin concentrations (will be discussed in section
2.2). With a low intake during early lactation, heavier sows are not able to meet
lactation requirements. As a result, increasing feed intake during gestation leads to the
same common reproductive problems after their first weaning, which are a reduction
of ovarian activity extending the weaning-to-oestrus intervals and lower ovulation
rates leading to smaller sizes of subsequent litters. (Boyd et al., 2000b; Quesnel et al.,
1998a).
1.2.2 Influence on lactation feed intake by metabolic hormones
Feed intake is controlled by the hypothalamus and the decrease in feed consumption
during early lactation is associated with several mechanisms in lactating sows.
However, the main indicators and effectors of metabolic regulation are the
concentrations of circulating insulin and leptin (Broberger, 2005).
1.2.2.1 Leptin
Leptin is the protein product of the obesity gene and is primarily produced by
adipocytes, where its synthesis and secretion are regulated by adipose tissue and body
7
mass across vertebrate species (Considine et al., 1996; Maffei et al., 1995). Circulating
leptin level in lactating sows is positively correlated with backfat depth and dietary
energy intake during gestation (Estienne et al., 2000; 2003), but is negatively
correlated with feed intake during lactation (Revell et al., 1998). Loftus (1999)
reported that leptin secretion is stimulated by body energy balance and acts on the
hypothalamus to control appetite. This finding indicates that increased feed intake
during pregnancy causes sows to have a high body fat mass at farrowing together with
a higher blood leptin concentration, and this high leptin level acts on hypothalamus to
suppress feed intake during lactation. The resulting lower feed intake after farrowing
causes body reserve mobilisation and the losses of body weight during lactation,
eventually impacting post-weaning reproductive performance.
1.2.2.2 Insulin
Another metabolic hormone that influences feed intake is insulin. Insulin is
synthesized and secreted by pancreatic beta cells as an immediate response to feed
intake in order to store excess consumed energy (Polonsky et al., 1988). Despite the
changes in circulating insulin level that occur after feed intake, there is a basal level of
secretion that is positively correlated with adiposity (Bagdade et al., 1967), which
reflects the amount of body reserves or metabolic status in an animal. It has also been
demonstrated in different species of animals that insulin modulates body energy
balance via the central nervous system (Menendez and Atrens, 1991; Woods et al.,
1979), resulting in a gradual and sustained reduction in food intake with increased
body weight. In some studies, sows were fed to a higher feed level during gestation
resulting in fat sows prior to farrowing as mentioned above, indicating a negative
correlation between feed intake and insulin resistance (or glucose intolerance) during
8
lactation (van der Peet-Schwering et al., 2004; Weldon et al., 1994; Xue et al., 1997).
The reduction in feed intake is likely affected by decreased pancreatic beta cells
sensitivity to high blood glucose concentrations. The insufficient insulin secretion
causes prolonged elevation in blood glucose concentration after feeding, and this may
delay the appetite of sows for the subsequent meal. This is, therefore, insulin resistance
may increase mobilization of body reserves to support maternal energy demands
during lactation that can compromise indirectly or directly a sow’s post-weaning
reproductive performance such as its weaning-to-oestrus interval (Koketsu et al.,
1996a) and/or its ovulation rate (Vinsky et al., 2006), eventually decreasing the
longevity of the sow (Koketsu et al., 1998).
Metabolic hormones are related to feed intake level during lactation in terms of
metabolic status prior to weaning. Leptin and insulin have been also emphasized as
potential mediators to influence post-weaning reproduction. This part will be discussed
in a later section.
1.2.3 Effect of body reserves change on reproductive performance
Back fat and body weight loss during lactation is associated with a poor post-weaning
reproductive performance, and is likely to extend the re-mating interval after weaning.
The influences of metabolic state after weaning on pregnancy rate, embryo survival
and second litter size have been reported in primiparous sows (Quesnel et al., 2005b;
Schenkel et al., 2010; Thaker and Bilkei, 2005; Vinsky et al., 2006; Whittemore,
1996), and these detrimental effects may increases culling rates (Hughes et al., 2010),
eventually compromising sow longevity in the breeding herd under commercial
conditions (Lucia et al., 2000). Hoffmann and Bilkei (2003) reported that minimising
9
body weight loss during lactation can improve post-weaning reproductive
performance; moreover, even with similar body weights losses during lactation,
primiparous sows had longer weaning-to-oestrus interval than mature sows (Thaker
and Bilkei, 2005). The authors also indicated that sow body weight losses < 15 %
during lactation did not extend the weaning-to-oestrus interval (< 7 days); however,
the subsequent litter sizes was compromised when sows lost > 10 % body weight
during lactation. This is consistent with Schenkel et al. (2010), who found a significant
decrease in size of the second litters when sow body weight loss was > 10 % during
lactation in during their first lactation, but no effect on oestrus return intervals after
weaning. Patterson et al. (2011) reported that optimal body weight is recommended to
be > 178 kg at weaning (Landrace x Large White) and the subsequent number of
piglets born was decreased when sows’ body weights were < 178 kg at weaning. A
similar finding was reported in Clowes et al. (2003a), suggesting that a proper weaning
body weight is around 180 kg and a backfat thickness of 13.5 mm in Camborough ×
Canabrid primiparous sows. It is likely that post-weaning reproductive performance is
impacted by the certain level of body reserve mobilization during lactation, but is also
determined by the optimal body reserves at farrowing to act as a buffer against either a
reduction of body reserves or low feed intake during lactation.
1.3 Mechanism of energy balance effects on reproductive performance
1.3.1 Energy deficiency and reproductive performance interactions
Relative changes in the quantity or quality of the lactation diet either over the whole of
lactation or at a critical stage (final week of lactation) to investigate reproductive
efficiency in primiparous sows have been well documented. In first lactation sows,
most researchers determined that insufficient nutritional intake (energy or protein
10
deficit) accompanied by severe catabolism can cause detrimental effects on follicle
development, oocyte quality, ovulation rate and embryo survival (Ashworth et al.,
2009; Foxcroft et al., 2007), or as an alternative measure, the size of the subsequent
litter. However, most of the studies over the past 20 years that investigated the effects
of feed level during lactation on primiparous sows showed varying effects of feed level
during lactation, with sometimes effects on interval to oestrus, sometimes on ovulation
rate and/or embryo survival; particularly, the effect of feed level during lactation on
weaning-to-oestrus interval tended to be less pronounced from studies over the last ten
years as shown in Table 1.2 (adapted from Prunier and Quesnel (2000b)).
The figures in the Table 1.2 show that, over the last 10 years, the weaning-to-oestrus
interval has improved for both well-fed and feed restricted sows. Also, the weaning-to-
oestrus interval between high and low treatments did not differ by feed level within
studies regardless of the level of feed intake during lactation. This improvement in the
weaning-to-oestrus interval could be caused by genetic selection for a short weaning-
to-oestrus interval by the pig industry; however, feed restricted sows may still have a
prolonged interval from weaning to ovulation. On the other hand, the substantially
delayed weaning-to-ovulation interval in feed restricted sows may benefit, at least
partly, follicle development during this extended period. This change may probably
explain most of findings which showed no significant effects on ovulation rate.
However, the metabolic mechanisms that influenced folliculogenesis in those studies
remain unclear.
That most restricted-fed sows showed no difference in weaning-to-oestrus interval
and/or ovulation rate could be due to the weight of modern first litter sows at
11
farrowing (around 190 kg) and that they were standardised to litters of 9-10 piglets;
also, the percentage of body weight loss during lactation for the sows fed low feed
levels were around the threshold (< 15 %) of detrimental effects on post-weaning
reproductive performance. Alternatively, the results from these recent studies indicated
that less severe feed restriction, specifically for the sows that were only restricted
during the last week of lactation, may not have enough energy challenge to affect the
weaning-to-oestrus interval and/or ovulation rate. However, the feed restriction may
still impact on embryo survival in those modern primiparous sows. A severe negative
energy balance was associated with impaired folliculogenesis and low embryo survival
by Zak et al. (1997a), although the findings in recent studies did not show a clear
significant tendency. Presumably, genetic selection has improved the weaning-to-
oestrus interval, but more studies are necessary to elucidate whether a catabolic state
arising from a negative energy balance during the last week of lactation or whole
lactation period clearly does impact the ovulation rate and embryo survival in modern
primiparous sows.
Table 1.2 Feed levels during lactation on subsequent reproductive performance in young sows
Reference Duration, days
Litter size
Feed intake ratio, %
Body weight loss, %
WOI, days
Ovulation rate Embryo survival, %
High Low High Low High Low High Low High Low Kirkwood et al., 1990 28 - 80 40 7 14 6.0 8.9* 17.6 17.7 83 72* Baidoo et al., 1992 28 9-10 70 37 7 18 5.9 7.3* 16.4 17.2 81 67* Zak et at., 1997a x 28 6 80 45 5 10 3.6 5.1* 19.9 15.4* 88 64* Zak et al., 1998 28 8-10 95 47 9 22 4.2 6.3* 14.4 15.6 83 72 Quesnel and Prunier., 1998 24 9-11 95 63 5 11 5.7 5.9 19.2 20.7 - - Mao et al., 1999 x 28 9 79 37 10 15 4.6 5.1* 17.7 16.7 67 73 Van den Brand et al., 2000c 22 9 90 67 8 14 5.1 5.4 18.1 16.2* 70 68 Vinsky et al., 2006 x 21 9 79 42 2 7 5.3 5.4 18.3 18.2 79 68* Patterson et al., 2011 x 20 10-12 90 60 4 11 5.0 5.3 19.7 20.2 71 70
1. High=control; Low=feed restriction; WOI= weaning-to-oestrus interval
2. Feed intake ratio is calculated between actual energy intake and requirement for maintenance + milk production in lactating sows. If the
ratio was not provided in the source papers, the equation used is: 0.46 Χ body weight (kg) 0.75 + 28.59 Χ daily litter gain (kg) – 0.52
(after Noblet et al. 1999). In Patterson et al., 2011 study, control and restrict sows were fed at 90% and 60% of appetite from 7 days
before weaning.
x Restricted feeding during last week of lactation
*Indicates a significant difference within criteria (P <0.05).
13
1.3.2 Follicle recruitment and development, ovulation rate and embryo survival
Typically, follicle diameter is around 2-5 mm during late lactation (the stage of follicle
recruitment). Once the suppressive effects of lactation are removed at weaning (piglets
sucking), the recruited follicles will rapidly start growing (selection) (Cox and Britt,
1982). Sows come into oestrus with follicle diameters around 6-7 mm (Liu et al.,
2000) and these larger follicles (dominant follicles) develop to pre-ovulatory size (7-9
mm) before ovulation (Soede et al., 1998). Quesnel et al. (1998b) observed that feed
restriction at a level of 50 % of ad libitum suppressed antral follicle development in
lactating primiparous sows, as compared to well-fed sows that had a higher proportion
of antral follicles in the 1.0-2.9 mm size at weaning. The average number of (selected)
follicles > 4 mm was 6.8 for the restricted-fed sows, compared to 12.2 for the well-fed
sows at two days after weaning.
Sows that lost less body weight during lactation have been reported to have a greater
number of larger follicles after weaning that contained more follicular fluid (Clowes et
al., 2003a). The authors found a positive correlation between the numbers and
diameters of follicles, also associated with quality of the oocytes to undergo pre-
ovulatory maturation and fertilization in vitro. The finding is consistent with earlier
observations that increasing catabolism (sows fed 50 % of ad libitum) during the last
week of lactation nutritionally induced alterations in the quality of follicular fluid and
oocytes (Zak et al., 1997b) and in the ovulation rate (Zak et al., 1997a). The number of
larger follicles in the pre-ovulatory pool and the quality of oocytes may be affected via
the nutritional intake during lactation (Clowes et al., 2003a), alternatively, may
influence the ovulation rate (Yang et al., 2000a) and embryo survival (Zak et al.,
1997a). The increased loss of embryos before Day 30 after mating could be, at least in
14
part, the consequence of timing feed restriction during the final stage of oocyte
maturation (Foxcroft, 1997) resulting in reduction of oocyte quality. Moreover, Soede
et al. (1998) indicated that follicle size at ovulation is related to luteal development at
Day 5 of ovulation. This may have influences on embryo survival due to inadequate
circulating progesterone concentration and extend the effect into later pregnancy, and
ultimately determine subsequent litter size. Therefore, in primiparous sows,
undernutrition during lactation may coincide with a critical window during which
nutritionally influences oocyte quality and maturation, and ovulation rate, and could
cause detrimental effects on embryo survival during early pregnancy.
1.3.3 Pre- and post-weaning gonadotrophin changes and follicle development
1.3.3.1 Pre-weaning gonadotropic secretion
During lactation, piglet sucking suppresses luteinising hormone (LH) secretion via the
hypothalamic-pituitary-ovarian axis. The hypothalamus secretes gonadotrophin-
releasing hormone (GnRH) in a pulsatile manner to stimulate the anterior pituitary for
LH secretion (De Rensis et al., 1993). Circulating LH remains low and stable during
early lactation which prevents advanced antral follicle growth (Sesti and Britt, 1994;
Varley and Foxcroft, 1990); however, LH secretion starts to increase slightly in terms
of a reduction of suckling stimulus during late lactation (Quesnel and Prunier, 1995)
and, at least in part, the increase in pituitary LH response to GnRH release
(Rojanasthien et al., 1987). Once the ovarian follicle pool responds to LH pulsatility,
some larger follicles have been observed in sows at weaning but the follicle diameters
do not grow beyond 3-4 mm (Lucy et al., 2001). In contrast to LH, the role of follicle-
stimulating hormone (FSH) during lactation is as an inducer of follicular recruitment
which is more associated with early follicular development. FSH on one hand and
15
oestradiol and inhibin concentration changes on the other are negatively correlated,
which explains why, with an increase in circulating oestradiol and inhibin from
recruited follicles, circulating FSH decreases in late lactation (ovarian negative
feedback). Lucy et al. (2001) suggested that follicle turn-over was related to temporary
FSH concentration changes during lactation and is necessary for recruitment of antral
follicles.
1.3.3.2 Post-weaning gonadotropic secretion
A high LH pulse frequency with low amplitude and increased basal concentration is
generally demonstrated after weaning (Foxcroft et al., 1987; Zak et al., 1998). The
increase in LH induces the growth of antral follicles toward pre-ovulatory size (Lucy
et al., 2001). Concentrations of FSH initially increase after weaning then decrease
around two days later as inhibin increases during the follicular phase (Wheaton et al.,
1998). This reduction in FSH concentration terminates growth of small and medium
sized follicles and only large follicles respond to LH during the pre-ovulatory period
(Lucy et al., 2001). Oestradiol concentration increases rapidly after weaning because
of the ongoing selection of larger follicles in the ovaries. Meanwhile, the increased
oestradiol level causes a negative feedback on the hypothalamus, reducing both FSH
and LH secretions, but FSH release is mainly suppressed by inhibin before pre-
ovulatory FSH and LH surges (Soede et al., 2011). Ongoing increased oestradiol
concentration triggers the FSH and pre-ovulatory LH surges by positive feedback.
Ovulation normally commences at on average 30 h after the peak of LH surge and the
ovulation process only takes 1-3 hours (Soede et al., 1998). The follicle diameter at
ovulation is between 6 mm to 8 mm (Lucy et al., 2001; Soede et al., 2011), and the
16
variation of follicle diameter can be affected by parity of the sows, metabolic status at
weaning and experimental treatments during pre- and post- weaning.
1.3.3.3 Nutrition and gonadotropins
Undernutrition during lactation in sows leads to a reduction of LH pulsatility after
weaning and postponed weaning-to-oestrus interval (van den Brand et al., 2000a).
Also, insufficient nutrition and negative energy balance cause the ovarian follicles to
be less responsive to LH pulses pre- and post-weaning (Kauffold et al., 2008; Koketsu
et al., 1998; van den Brand et al., 2000a). Thus follicular recruitment and development
is depressed in lactating sows at the later stage, resulting in a small follicle size at
weaning and delayed follicle development and oestrus after weaning (Bracken et al.,
2006; van den Brand et al., 2000a). Moreover, inadequate nutrition during lactation
has a similar impact on follicle development through depressed FSH concentration. A
recent study reported that plasma FSH concentration at day 15 and 18 post-farrowing
was clearly impacted by feed restriction (Kauffold et al., 2008). The results showed
that a decreased FSH concentration resulted in a mean follicle diameter of
approximately 2 mm at Day 20 in restricted-fed lactating sows, while there was an
increase in follicle diameter in sows that were fed ad libitum within the same time
interval. It is likely that the FSH and LH are both acting on ovaries to stimulating
follicle growth during lactation particularly during late lactation and at the time of
weaning. This suggests that nutritional effects could change follicle recruitment and
development through the medium of gonadotrophinic action at ovarian level, and
eventually determine the ovulation rate. However, the mechanisms of action of the two
gonadotrophins - LH and FSH, on folliculogenesis prior to weaning are still not fully
understood.
17
1.3.3.4 Progesterone
Progesterone is produced by corpora lutea (CL) after ovulation has occurred and the
concentration of progesterone is (partly) dependent on the number of CL as the source
of secretion during early pregnancy (Willis et al., 2003). A sufficient concentration of
progesterone is necessary for the maintenance of pregnancy. After ovulation has
occurred, circulating progesterone concentration rises up to Day 14 (57.9 nmol/l) in
gilts and then decreases gradually in the peripheral concentration from Day 14 to 20
(56.0 nmol/l) (King and Rajamahendran, 1988). The plasma progesterone level
remained constant for the rest of sampling period (47.1 nmo/l) (King and
Rajamahendran, 1988). The authors reported that this reduction of progesterone
beyond Day 14 in pregnant pigs was associated with the basal prostaglandin
synthesized from the uterus, which may prevent the CL from reaching maximum
secretion.
Circulating progesterone concentration in early pregnancy is positively correlated with
ovulation rate (r = 0.52) (Willis et al., 2003). Almeida et al. (2001) reported that
inadequate feed intake during the luteal phase in a gilt model affects ovulation rate and
the progesterone rise after the LH surge. Similar effects were found in primiparous
sows that experienced a low feed intake during lactation, which had reduced plasma
progesterone concentration associated with poor embryo survival (Zak et al., 1997a;
Zak et al., 1998). Hence, negative effects of low feed level on ovarian activity may
reduce blood progesterone concentration during early pregnancy and reduce embryo
survival and suppress development.
18
1.3.4 Metabolic hormones and ovarian function
Nutrition influences effects of gonadotrophins on ovarian activity as described
previously, but metabolic mediators like insulin, insulin-like growth factor-I (IGF-I)
and leptin are also involved by synergy with gonadotropins or acting directly at the
ovarian level (Giudice, 1992; Poretsky and Kalin, 1987; van den Brand et al., 2001).
Low feed intake during lactation impacts on LH pulsatility, follicle development, and
ovulation rate (Booth et al., 1994; Quesnel et al., 1998b), in parallel with a decrease in
circulating glucose, insulin and IGF-I concentrations as well as leptin (Prunier and
Quesnel, 2000b). Thus, insulin and IGF-I may play a role by affecting ovarian cells
during a period of undernutrition, and decrease the responsiveness of the ovary to
gonadotrophins (Cox, 1997).
1.3.4.1 Insulin, IGF-I and glucose
Post-weaning reproductive performance has been associated with negative energy
balance of sows at weaning and the decline of circulating insulin, IGF-I, and glucose
concentrations (Koketsu et al., 1996b; Zak et al., 1997a), indicating that insulin and
IGF-I may mediate nutritional effects and stimulate follicle development directly at the
ovarian level. Precisely, insulin and IGF-I have been found to stimulate granulosa cell
mitogenesis and steroidogenesis of follicular cells during the follicular phase (Adashi
et al., 1985). Presumably, oocyte quality may therefore be impacted by a reduction in
insulin and IGF-I which is confirmed with the finding in a study by Tsafri and
Channing (1975)
In some studies, Insulin and IGF-I concentrations have been reported to be improved
by manipulating feed intake, feed composition (starch-rich diet) or by the
19
administration of insulin in pigs. In a gilt model with a high (3.5 kg/day) or low (1.35
kg/day) feed ration for 19 days during the oestrus cycle, a high feed intake increased
both systemic insulin and IGF-I concentrations (Ferguson et al., 2003). The high feed
level increased IGF-I and oestradiol in the follicular fluid resulting in an increased
percentage of oocytes at metaphase II in an in vitro maturation model, and improved
number of pre-ovulatory follicles. In primiparous sows, Zak et al. (1997a) and Prunier
and Quesnel (2000a) reported that feed restriction during lactation decreases
circulating insulin and IGF-I concentrations, and as IGF-I amplifies FSH action and is
associated with oocyte maturation, follicular recruitment and development may suffer
detrimental effects, thus leading to a decrease in follicle growth in feed-restricted sows
(Clowes et al., 2003a) and reduce ovulation rate (Quesnel et al., 1998b).
Moreover, insulin and glucose were lower before weaning in sows that were fed 40 %
of the diet compared to sows fed a high feed level throughout lactation (Koketsu et al.,
1996b). The authors also found that insulin and glucose concentrations were positively
correlated with LH pulse frequency and weaning-to-oestrus interval, which is in
agreement with van den Brand et al. (2000a), who reported the same for sows fed with
a starch-rich diet during lactation. Similar findings have been reported by Kemp et al.
(1995), suggesting feeding a starch-rich diet to lactating sows to induce an increase in
circulating insulin stimulates the pre-ovulatory LH surge.
In addition to enhancing insulin and IGF-I, to study ovarian physiology by dietary
manipulations, exogenous insulin has been studied as well. Cox et al., (1987) observed
an increased ovulation rate in response to an exogenous insulin treatment during early
follicular phase in gilts. Conversely, Quesnel and Prunier (1998) did not alter ovulation
20
rate in restricted-fed sows with exogenous insulin administration during late lactation.
Van den Brand et al. (2000a) reported that ovulation rate tended to be higher in sows
fed a high feed level than sows fed a low feed level throughout lactation. Therefore,
elevated circulating insulin, IGF-I and glucose concentrations via dietary
manipulations may have a more positive influence on folliculogenesis, and may thus
improve post-weaning reproduction.
1.3.4.2 Leptin
Circulating leptin concentration in sows at early stages of lactation has been shown to
be positively related to fat tissue mass (r = 0.70, P < 0.001) and feed intake (r =.-0.70,
P < 0.02) during lactation (Estienne et al., 2000; Robert et al., 1998). In a review by
Barb et al.(2008; 2001) reported that in well-fed sows during lactation, leptin has also
been reported to be positively correlated with plasma insulin and LH concentrations,
which reflects the metabolic status of sows at weaning. For example, circulating leptin
concentration has been shown to be positively related to fat reserves at weaning with
longer weaning-to-oestrus interval for sows that were fed 50 % of appetite from Day
22 to Day 28 of lactation compared with sows that were fed ad libitum for a 28 days
lactation period (Mao et al., 1999). The authors also demonstrated that at the day of
weaning, postprandial leptin concentrations were lower for restricted sows compared
to sows fed to appetite. Moreover, Barb et al. (2005) reported that GnRH release from
hypothalamic tissue and LH secretion from pituitary cells were increased by leptin in
vitro, suggesting leptin acts through the hypothalamus and may drive follicle
development via increased ovarian activity before ovulation (Quesnel et al., 2007).
Leptin seems to act as a metabolic signal and is correlated with adipose tissue, body
energy balance and LH secretion for sows; however, post-weaning reproductive
21
performance may also depend on other metabolic hormones such as glucose and
insulin concentrations during period of weaning.
1.4 Measures to counteract second litter syndrome
Reproductive failure after weaning in primiparous sows is generally considered to be
related to a low feed intake capacity coincident with an excess body weight loss from
limited body reserves during lactation. Attention has been paid to reducing body
reserve mobilisation during lactation and post-weaning maternal body recovery before
onset of oestrus in primiparous sows, in order to increase post-weaning reproductive
performance as well as subsequent litter size. Several sow management options during
lactation and post-weaning have been investigated in primiparous sows to overcome
the reproductive problems and also optimise litter size at their second parity. These
management strategies are not all included in the present studies, however some
mechanisms may be involved in the following experimental chapters. Hence, they are
discussed in the section below.
1.4.1 Pre-weaning repair strategies
1.4.1.1 Protein (lysine) supply
Increased dietary intake and/or energy level throughout lactation are known to affect
the body condition of lactating sows and post-weaning reproductive performance
(Beyer et al., 2007; Boyd et al., 2000b). Lysine is considered to be the first limiting
amino acid in the diet and daily lysine intake is a primary determinant of sow
performance. A high lysine intake results in a reduction of body weight and backfat
losses during lactation (McNamara and Pettigrew, 2002; Yang et al., 2008). Moreover,
an increased in dietary lysine requirement has been reported by Yang et al. (2009),
22
suggesting modern primiparous sows require higher lysine intake (1.3 % of lysine)
during lactation which corresponds to a lysine requirement of 74 g/day to support body
maintenance and milk production, and may improve reproduction through increased
post-weaning LH pulsatility. This suggests that providing a higher amount of lysine in
the diet is essential to meet lactation requirements and also to increase potential
reproductive performance in modern first litter sows.
1.4.1.2 Energy sources
Potential solutions for the gap between actual energy demands and lower feed intake
capacity during lactation in primiparous sows have been extensively researched.
Studies indicate that increasing energy density during lactation can be an approach for
overcoming limited appetite in primiparous sows to minimise the negative energy
balance at weaning. In practice, lactational dietary energy was increased by varying the
fat content of diets as an approach to reduce mobilisation of body reserves during
lactation. However, a high fat content in the lactation diet may reduce feed intake
(Renaudeau et al., 2001), and has also not been found to improve sow body condition
and the weaning-to-oestrus interval (Heo et al., 2008). Similarly, Quiniou et al. (2008)
reported that sows fed a fat-supplemented diet lost more backfat during lactation,
which corresponds to an acceleration of negative energy balance as reported by van
den Brand et al. (2000b). This may explain that a high energy source that is supplied
by lipid only has beneficial effects on piglet growth (van den Brand et al., 2000a) as
most fatty acids are drained to the mammary glands (Jones et al., 2002).
In contrast to fat as an energy source, increasing energy intake by providing a starch-
rich diet throughout lactation has been investigated by van den Brand (2000a). The
23
authors showed that the number of LH pulses was higher during lactation and follicle
size at Day 2 after weaning slightly larger in sows on the starch-rich diet, but weaning-
to-oestrus and ovulation rate were unaffected. Furthermore, they induced a higher
circulating insulin concentration which may favour reproductive characteristics, since
insulin acts as a key hormone to mediate between nutrition and reproduction. Increased
circulating insulin concentration can potentially stimulate LH secretion after weaning
(Quesnel et al., 1998b) and improve follicle development via increased ovarian
activity before ovulation (Quesnel et al., 2007), as well as embryo survival through
increased progesterone level during early gestation (Kemp et al., 1995).
1.4.1.3 Reduced suckling
The metabolic status of sows in the common range of a 3 to 4 week lactation length is
related to post-weaning reproduction, and can possibly be improved by decreasing
milk production demands through reducing sucking load or intensity during late
lactation. In techniques such as intermittent suckling and split-weaning, the effects on
ovarian activity, circulating gonadotrophins, reproductive performance and fertility
have been widely studied (Gerritsen et al., 2008b; Kugonza and Mutetikka, 2005;
Langendijk et al., 2009; Zak et al., 2008). In intermittent suckling, suckling is
interrupted by a temporary removal of the whole litter usually for a 10 to 12 hours
period each day when piglets are old enough to eat creep feed. Another management
technique that reduces the suckling stimulus preceding weaning is split-weaning. In
split-weaning, half (or part) of the litter is permanently removed while the smaller
piglets are left sucking.
24
Reducing the number of piglets may alleviate mobilisation of maternal body reserves
before weaning and minimise the weaning-to-oestrus interval. Recent reports indicate
that split-weaning acutely increases circulating FSH (Degenstein et al., 2006)
accompanied with increased LH concentrations (Zak et al., 2008). This partly breaks
down the inhibition of gonadotrophin secretion during late lactation and would be
anticipated to stimulate follicle development and a shorter weaning-to-oestrus interval
after weaning (Zak et al., 2008). The results on weaning-to-oestrus interval were not
confirmed by Vesseur et al. (1997) who found only a small influence of split-weaning
on the weaning-to-oestrus interval in first litter sows and no effect on subsequent litter
size. These conflicting findings may be partly due to the critical period of separation,
genetic differences and sow metabolic status during the period of experiments.
Another approach to improve negative energy balance during lactation is interrupted
suckling. Additional to improvement of sow body conditions at weaning, a similar
effect as split-weaning on gonadotrophin patterns and follicle development were
observed during lactation (Gerritsen et al., 2008a; Langendijk et al., 2009). With
interrupted suckling, however, the effect on gonadotrophin secretion is much more
dramatic, allowing pre-ovulatory follicle development and ovulation during lactation
in a percentage or even a majority of sows depending on genetics and parity. For
alleviation of metabolic and suckling pressure alone, interrupted suckling would have
to be applied for a shorter period than in studies referred to above. Interrupted suckling
and split-weaning can potentially improve post-weaning reproductive performance,
however, when applying these techniques there is a risk of lactational oestrus at
unpredictable times.
25
1.4.2 Post-weaning repair strategies
1.4.2.1 Nutrition or insulin administration
The recommendation of feed level after weaning is generally to supply feed ad libitum
to overcome the negative energy balance and improve sow post-weaning reproductive
performance, however, the improvement is limited. In fact, modern pig genotypes
seem to be having less of an improvement on reproduction performance in the form of
ovulation rate and embryo survival in both gilts and in sows if the pigs are provided
with a high feed level after weaning and before mating. Data to support this were
reported by Ferguson et al. (2006), who found that feeding levels at 1, 1.8 and 2.6
times maintenance prior to insemination did not affect ovulation rate and embryo
survival at Day 27 of pregnancy in gilts. This is consistent with no significant effect of
post-weaning feed intake observed in the restricted-fed sows as shown by Baidoo et al.
(1992).
However, increased circulating insulin concentration after weaning could be another
way to address catabolic status in weaned sows. Ramirez et al. (1997) reported that
manipulation with exogenous insulin treatment from weaning to increase post-weaning
circulating insulin concentration, and suggested that sows mated within 7 days after
weaning and treated with insulin for 4 days had one more piglet in the second litter
compared to controls (10.3 vs 9.3 piglets). A more recent study indicates that Wientjes
et al. (2011) indicated that sows fed a dextrose- plus lactose-containing diet from
weaning to ovulation showed a positive relationship between post-weaning plasma
insulin concentration and progesterone level (β = 0.14 (ng ⁄ mL) ⁄ (IU ⁄ mL); P = 0.05)
during the first 10 days of pregnancy. Besides, extra benefit in weaned sows fed an
insulin-stimulating diet (dextrose, 150 g/day) during the pre-mating period has been
26
found to increase uniformity of piglet birth weight within litters (van den Brand et al.,
2006). A similar finding was found by van den Brand et al. (2009) in a later report,
demonstrating sows that received a supplement with dextrose (150 g/day) plus lactose
(150 g/day) from weaning to insemination potentially reduced the birth weight
variation within litters. Improving piglet uniformity could reduce piglet mortality
during the first week of lactation through more equal distribution of colostrum and
thus improve piglet survival during lactation (Devillers et al. 2007). There are
indications that insulin and IGF-I concentrations are elevated via a carbohydrate diet
and stimulate, at least in part, oocyte and follicle development via LH and/or directly
at the ovarian level. Alternatively, embryo survival may be also improved by a higher
progesterone levels through beneficial effects of insulin-stimulating diets.
1.4.2.2 Skip-a-heat and altrenogest administration
Extension of the weaning-to-serving interval may also be achieved by “skip-a-heat” or
oral progestagen treatment (Regumate®) to allow first litter sows to recover from
lactational metabolic stress and thereby increase sow reproductive performance. The
skip-a-heat technique involves leaving a sow unmated until the second oestrus. Clowes
et al. (1994) studied the effects of skipping the first heat after weaning on metabolites
and hormone changes and subsequent litter size. The data showed that litter size in the
second parity was increased by 2.6 total born piglets and 2.9 piglets born alive piglets
in sows that were served at the second rather than at the first oestrus after weaning.
This is in accordance with the findings of Patterson et al. (2006) who re-studied the
skip-a-heat effects in weaned sows and observed 2.3 more live embryos and higher
embryo survival (77.4 vs 68.1 %) in sows inseminated at second oestrus. Similarly,
using oral progestagen treatment postpones the post-weaning oestrus and gives extra
27
days to weaned sows for physiological recovery by extending the weaning-to-serving
interval. Positive findings were reported in sows that had oral progestagen treatment
by Patterson et al. (2008), who suggested that altrenogest administration successfully
improved the ovulation rate and embryo survival, and synchronised the return to
oestrus in weaned sows. Although the goals of “skip-a-heat” and oral progestagen like
Regumate may be similar, Regumate treatment seems to be a possible technique to
apply in commercial conditions compared to the skip-a-heat strategy. Oral progestagen
has more advantages as progestagen postpones formation of pre-ovulatory follicles
after weaning and synchronises the return to oestrus without incurring the cost of the
additional non-reproductive days for the duration of one oestrous cycle. The costs of
Regumate treatment obviously have to be offset by increased reproductive
performance.
1.5 Aim of this thesis
Studies have clearly shown that primiparous sows have more difficulty to overcoming
the burden of their first lactation and achieving their potential post-weaning
reproductive performance. This problem has been related to maternal body weight
losses (negative energy balance) during lactation, but the outcome of post-weaning
reproduction traits varies between studies during the last 10 years. It is necessary to
have a better understanding of the reproductive mechanisms of energy metabolism and
its effects on ovarian activity, metabolic hormones and gonadotropins in modern
primiparous sows. The aim of the thesis was to evaluate the causes of reproductive
problems at second parity in modern genotype sows and manipulate dietary energy as
a feeding strategy during the critical period to improve post-weaning reproductive
performance and subsequent litter size.
28
In our knowledge, reproductive performance in primiparous sows has been related to a
limited feed intake capacity, resulting in excess body weight loss during lactation and
causing second litter syndrome. Chapter 2, therefore, investigates reproductive
performance at an Australian commercial pig farm (an on farm survey) to develop a
clear of view of practical circumstances and the associations between post-weaning
reproductive performance and body weight loss during lactation or body weight at
weaning, and subsequent litter size. Subsequently, different energy levels were
provided during the pre- and follicular phases using an experimental gilt model in
Chapter 3, to study the carry-over effects on follicle recruitment, ovulation rate, quality
of luteal tissue and embryo survival. A critical period was identified showing that
energy deficiency during early antral follicle development could have a detrimental
impact on ovulation rate and number of embryos. Further, if a limited feed intake
capacity reduces post-weaning reproductive outcome in primiparous sows, an
increased dietary energy density during lactation might be an option to reduce the
catabolic status at weaning. Hence, in Chapter 4, energy substitutions were designed to
increase dietary energy level or alternatively, to increase by circulating glucose and
insulin profiles, and provided as top dressing during the last week of lactation to
stimulate ovarian activity during the critical period of early antral follicle development.
Based on the significant outcomes of pre-weaning dietary substitutions from Chapter
4, Chapter 5 studied follicular development and endocrine characteristics using the
same feeding strategy and energy substitutions and, also a post-weaning Regumate
treatment during the same window to improve subsequent litter size. In the final
chapter of the thesis (Chapter 6), the results from all experimental chapters will be
discussed with up-to-date acquired knowledge from studies.
29
Chapter 2
Comparison of maternal body condition changes
during lactation and status at weaning on
subsequent reproductive performance in
primiparous sows: on-farm survey
30
Chapter 2
2.1 Introduction
Inadequate nutrient supply causes excessive mobilisation of maternal body reserves
during lactation and affects subsequent reproduction in primiparous sows (Clowes et
al., 2003a; Yang et al., 2009). In general, modern lean first-litter lactating sows have
low backfat levels and feed consumption and are less capable to meet their high
nutrient demands for lactation than multiparous sows. Consequently, the negative
energy balance during lactation results in maternal body reserve loss (Kim and Easter,
2001) and may possibly impact subsequent reproductive performance (Soede et al.,
2000). Retrospective studies suggest that post weaning reproductive performance is
substantially compromised when a sow loses more than 10 % body weight during
lactation (Thaker and Bilkei, 2005).
Excessive loss of body reserves during lactation not only influences pregnancy rate
and litter size of the next reproductive cycle (Quesnel et al., 2005b) but also increases
culling rate (Hughes et al., 2010) and eventually impacts on longevity in the breeding
herd (Lucia et al., 2000). Although feed is provided on an ad libitum basis to
encourage lactation intake, lower post-weaning reproductive performances is still
occurring in most commercial pig farms in Australia (Australian Pork Ltd, 2010). The
objective of this on-farm survey was to provide a clear indication of the current
situation on a commercial pig farm by assessing the relationship between changes in
body reserves during lactation and their status at weaning with the extent of any
impairment in subsequent reproductive performance in primiparous sows.
31
2.2 Methods
The study was designed to assess the relationship between body reserve changes
during lactation and/or body status at weaning on post-weaning reproductive
performance in primiparous sows in a commercial piggery (Australian Pork Farms;
APF) at Wasleys in South Australia (34° 26' 38.26"S, 138° 36' 53.01"E). This survey
ran from May through August in 2009, and the averages of maximum and minimum
temperatures were 17 °C and 7 °C respectively (Bureau of Meteorology, Australian
Government) during the data collection period.
2.2.1 Animals, housing and feeding
A total of 218 Large White first-litter sows (in 10 batches) at the Wasleys piggery
were included in this study. Pigs from the same batch were housed in individual
farrowing crates and kept in the same farrowing shed. All gilts were fed ad libitum
with a lactation diet containing 14.2 MJ of DE/kg, 20.0 % CP, and 1.2 % Lysine (on
an as-fed basis). Access to water during lactation was ad libitum through individual
nipple drinkers in each farrowing crate. The duration of lactation was on average 28.6
± 1.1 day with 8 - 11 piglets suckled at the start of lactation and on average 9.1 ± 1.4
piglets weaned.
2.2.2 Measurements
Body weight and P2 backfat depth (P2 ; 6.5 cm from the mid line at the head of the last
rib) were measured after feeding on d 1 post-farrowing and one day before weaning. P2
was measured using a 3.5 MHz frequency ultrasonic device with a special backfat
probe (Aquila Pro Vet. Esaote Europe B.V., Maastricht, The Netherlands).
32
One day after farrowing, the total number of piglets born per sow was recorded.
Within 24 hours postpartum, suckled litter size was adjusted by the piggery staff using
cross-fostering. Litter weight was recorded after litter size adjustment and one day
before weaning, in order to determine the average daily gain (ADG) of litters during
lactation. Routine procedures (teeth and tail clipping, and iron injection) were
conducted within 24 h postpartum. Post weaning boar exposure was performed from
day 4 after weaning for heat detection. When sows were detected in heat in the
morning, artificial inseminations (AIs) were performed: one in the afternoon of the
same day, and one next morning. Weaning-to-first insemination interval (WAI) was
defined when sows received their first AI post weaning. Sows failing to come into post
weaning oestrus within 14 days were classed as anoestrous. Pregnancy failure was
recorded in sows which were classified as having no signs of pregnancy using
ultrasound at 30 days after last artificial insemination or which lost pregnancy during
gestation. Any pregnancy failures during gestation, subsequent litter sizes and litter
details were all extracted from the farrowing records used to determine reproductive
performance.
The feeding regimes from post-weaning throughout next gestation were undertaken in
accordance with the standard piggery protocols. All data from post weaning to the
subsequent farrowing was accessed via the piggery’s computer records.
2.2.3 Calculations and statistical analysis
Of the 218 sows enrolled in the study, 205 sows were available for analysis, and 185
sows were served after weaning. Sows were not served if they remained anoestrous (n
= 20) or because of other non-reproductive reasons (injury, lameness or death, n = 13).
33
Data were analysed using two models for sow body condition: a) sow body weight
changes during lactation and; b) sow body weight at weaning. The models were used
to analyse the relationship of these two parameters with post weaning reproductive
performance.
2.2.3.1 Model 1- sow body weight changes during lactation
In the first model (model 1), sows were classified according to sow body weight
changes during lactation, as this is the approach that most studies follow to assess
effects of lactational mobilisation on reproductive performance. Three groups were
defined, which were sows with 25 % highest body weight change (average 8.6 kg
gain), the intermediate sows (average -3.3 kg change), and the 25 % sows with the
lowest body weight change (average -14.5 kg loss). This model was used to analyse
body weight and P2 at farrowing and weaning, WAI and litter size, using a univariate
approach in the following ANOVA model: Y = μ + body weight loss. Pregnancy and
anoestrus rate for the three groups were compared using Chi-square.
2.2.3.2 Model 2 - Sow body weight at weaning
In the second model (model 2), sows were classified to either HEAVY (H) or LIGHT
(L) according to their body weight (BW) being greater or less than the average at
weaning (186.5 kg). Based on body weight change being less or greater than the
average change (-3.15 kg) during lactation, H and L sows was assigned to two sub-
groups. This resulted in a 2 x 2 stratification, allowing analysis of body weight at
weaning as a static factor (BWcat), and body weight change during lactation
(BWchange, dynamic factor), and the interaction between the two factors in the
following ANOVA model: Y = μ + BWcat + BW change + BWcat x BW change + e,
34
with Y being body weight at farrowing or weaning, P2, WAI, or litter size. Pregnancy
and anoestrus rate for the four groups were compared using Chi-square analysis.
Generalized Linear Models was used to evaluate the relationships between sow body
weight changes during lactation or body weight at weaning and sow WAI, litter weight
gain and subsequent reproductive performance. All statistical analyses were all
performed with the SAS (9.3 edition; SAS Institute Inc, NC). The statistical
significance of each dependent variable in the models was determined by using a
significance level of P less than 0.05. The results are presented as means ± s.e.
2.3 Results
2.3.1 Univarite effect of body weight change (model 1)
Sows were classified into three groups (25 % lowest body weight change,
intermediate, and 25 % highest body weight change) in this analysis to investigate the
effects of body weight change during lactation on subsequent reproductive
performance. Sows with the most body weight loss had the highest body weight at
farrowing (P < 0.001) and had lower body weight and P2 at weaning (r = 0.003; P <
0.001) (Table 2.1). There were no effects of body weight changes during lactation on
sow post weaning anoestrus rate (P > 0.05), WAI (P > 0.05), pregnancy failure (P >
0.05) and subsequent litter size (P > 0.05). Overall, sows gained 3 to 19 kg in the
highest group and lost 9.5 to 43.5 kg in the lowest group, and sows body weight
change in the intermediate group was between +2.5 kg and -9 kg during lactation.
Body weight change during lactation was approximately +4.6 %, -1.7 % and -7.3 % of
the body weight at farrowing in the highest, intermediate and lowest groups
respectively. The total number of sows that lost more than 10 % body weight during
35
lactation was only seven, of which three sows in highest group, two sows in lowest
group and two sows in intermediate group. Anoestrus rate and failure of pregnancy
rate during early gestation did not differ between sow groups (P > 0.05).
36
Table 2.1 Reproductive performance base on body weight loss during lactation
Maternal body weight changes
Item 25% highest (n=50) intermediate (n= 88) 25% lowest (n= 47) P- Values
Changes BW a, kg 8.5 ± 0.6 -3.3 ± 0.3 -14.4 ± 0.9 < 0.001 P2 backfat depth, mm 0.69 ± 0.37 -0.89 ± 0.2 -1.71 ± 0.31 < 0.001
Parturition BW, kg 185.5 ± 2.5 189.2 ± 1.7 196.3 ± 2.2 < 0.001 P2 backfat depth, mm 18.96 ± 0.40 19.38 ± 0.3 19.47 ± 0.45 0.618
Weaning BW, kg 194.0 ± 2.5 185.9 ± 1.7 181.8 ± 2.2 0.003 P2 backfat depth, mm 19.65 ± 0.41 18.48 ± 0.2 17.76 ± 0.36 < 0.001 WAI a 5.04 ± 0.32 5.14 ± 0.18 5.21 ± 0.28 N.S. Total Born in parity 1, no. 9.92 ± 0.35 10.87 ± 0.31 10.45 ± 0.28 N.S. Born alive in parity 1, no. 9.28 ± 0.32 10.36 ± 0.30 9.78 ± 0.29 N.S. Total Born in parity 2, no. 10.44 ± 0.49 10.94 ± 0.37 11.07 ± 0.53 N.S. Born alive in parity 2, no. 9.93 ± 0.49 10.24 ± 0.35 10.48 ± 0.51 N.S. a BW=body weight; WAI=weaning-to-AI interval.
37
2.3.2 Sow body weight change and body weight at weaning in a multivariate
model (model 2)
There was no interaction between body weight change during lactation and body
weight at the subsequent weaning for any of the variables that were analysed. Sows
that were heavier than average at weaning (HEAVY, H), were heavier (> 25.62 kg)
and had more backfat (> 0.85 mm) at farrowing than LIGHT sows. Also, sows that
were heavier than average at weaning had lost less body weight during lactation (-3.89
vs. -7.69 kg). Regardless body weight at weaning, sows that lost more body weight
than average during lactation were 10 to 12 kg heavier at farrowing, although at
weaning the difference was only 2.1 kg.
There was no effect of either body weight at weaning (P > 0.05) or body weight
change during lactation (P > 0.05) on post weaning reproductive performance (Table
2.2). The anoestrous rate (P > 0.05), pregnancy rate (P > 0.05) and subsequent litter
size (P > 0.05) were not influenced either by body weight changes during lactation or
body weight at weaning (P > 0.05) (Table 2.2). There were no interactions between
sow body weight at weaning and body weight changes on for any of the parameters
analysed.
38
Table 2.2 Reproductive performance base on sow body weight at weaning
Maternal body weight at weaning
HEAVY (> average) LIGHT (< average) P- values**
BW change during lactation
>-3.15 kg (n=49)
<-3.15 kg (n= 36)
>-3.15 kg (n= 44)
<-3.15 kg (n= 56)
Weaning BW BW change
Weaning BW b, kg 203.9 ± 1.6 199.8 ± 1.7 175.7 ± 1.1 172.9 ± 1.2 < 0.001 0.021 P2 backfat depth, mm 19.73 ± 0.38 18.37 ± 0.46 18.31 ± 0.35 18.03 ± 0.26 0.014 0.032 Parturition BW, kg 198.7 ± 1.6 208.9 ± 1.8 172.1 ± 1.4 184.2 ± 1.4 < 0.001 < 0.001 P2 backfat depth, mm 19.63 ± 0.38 19.79 ± 0.55 18.18 ± 0.41 19.53 ± 0.36 0.040 0.057 Changes BW, kg 5.2 ± 0.8 -9.1 ± 0.7 3.5 ± 0.7 -11.2 ± 0.9 0.032 < 0.001 P2 backfat depth, mm 0.09 ± 0.38 -1.42 ± 0.38 0.13 ± 0.35 -1.50 ± 0.26 0.958 <0.001 WAI b 5.31 ± 0.37 5.31 ± 0.35 4.89 ± 0.21 5.05 ± 0.19 N.S. N.S. Total Born in parity 1, no. 10.22 ± 0.37 10.66 ± 0.41 10.40 ± 0.38 10.42 ± 0.33 N.S. N.S. Born alive in parity 1, no. 9.53 ± 0.34 10.05 ± 0.40 9.68 ± 0.38 9.94 ± 0.33 N.S. N.S. Total Born in parity 2, no 10.49 ± 0.53 11.12 ± 0.64 10.97 ± 0.52 10.82 ± 0.43 N.S. N.S. Born alive in parity 2, no 9.79 ± 0.54 10.52 ± 0.63 10.46 ± 0.45 10.16 ± 0.41 N.S. N.S.
a BW=body weight; WAI=weaning-to-AI interval.
** No significant interaction between sow BW at weaning and BW changes during lactation
39
2.3.3 Litter growth during lactation and subsequent litters
On average sows suckled 9.7 piglets at the start of lactation, and weaned on average
9.1 piglets. Litter size and daily gain (ADG) was higher in sows with 25 % most body
weight loss, compared to sows with intermediate body weight change and the 25 %
least body weight loss (model 1; Table 2.3). Similarly, in model 2 sows with more than
average body weight loss (catabolic sows) had a greater litter size and litter weight
gain during lactation, regardless body weight at weaning. Body weight at weaning was
not related to litter ADG. Weaning rate did not differ between groups (P > 0.05; Table
2.3; 2.4).
2.3.4 Correlations
Sows that were heavier at farrowing lost more body weight during lactation (r = -0.29,
P < 0.001) but body weight loss was not related to P2 at farrowing in the present study.
Body weight change during lactation was also related to body weight (r = 0.26, P <
0.001) and P2 at weaning (r = 0.27, P < 0.001). Body weight loss and P2 loss were also
related (r = 0.39, P < 0.001). Change in P2 was related to sow body weight (r = -0.18,
P = 0.008) and P2 (r = -0.56, P < 0.001) at farrowing, and P2 at weaning (r = 0.32, P <
0.001). Sow body weight and P2 at farrowing were both related to sow body weight (r
= 0.84, P < 0.001; r = 0.16, P = 0.021) and P2 (r = 0.23, P < 0.001; r = 0.60, P <
0.001) at weaning. WAI was not related to any variables in this study. Litter ADG was
related to change in sow body weight (r =-0.37, P < 0.001) and change in P2 (r =-0.29,
P < 0.001), and P2 (r = -0.21, P = 0.002) at weaning.
40
Table 2.3 Litter performance during lactation base on sow body weight loss
Maternal body weight changes
Item 25% highest
(n=50)
Intermediate
(n= 88)
25% lowest
(n= 47) P- Values
Litter size at beginning, no. 9.1 ± 0.1 9.8 ± 0.1 10.1 ± 0.1 <0.001
Litter size at weaning, no. 8.4 ± 0.2 9.1 ± 0.1 9.4 ± 0.2 <0.001
Litter weight at beginning, kg 13.21 ± 0.30 14.49 ± 0.24 15.19 ± 0.36 <0.001
Litter weight at weaning, kg 60.48 ± 1.69 67.35 ± 1.25 74.29 ± 1.61 <0.001
ADG b, kg/litter/day 1.65 ± 0.05 1.84 ± 0.04 2.07 ± 0.05 <0.001
Weaning rate, % 93.17 ± 1.88 93.24 ± 1.24 93.30 ± 1.58 0.953
a Gain= top 25 % of sows body weight changes; Loss= last 25 % of body weight changes; Medium= sow body
weight changes between Gain and Loss
b ADG= average daily gain
41
Table 2.4 Litter performance during lactation base on sow body weight at weaning
Maternal body weight at weaning
HEAVY (> average) LIGHT (< average) P- values**
BW change during lactation >-3.3 kg
(n=49) <-3.3 kg (n= 36)
>-3.3 kg (n= 44)
<-3.3 kg (n= 56)
Weaning BW
BW change
Litter size at beginning, no. 9.4 ± 0.2 10.1 ± 0.2 9.5 ± 0.2 9.9 ± 0.1 0.664 0.005
Litter size at weaning, no. 8.7 ± 0.2 9.4 ± 0.2 8.6 ± 0.2 9.3 ± 0.1 0.490 <0.001
Litter weight at beginning, kg 13.82 ± 0.34 14.52 ± 0.43 13.96 ± 0.19 14.92 ± 0.29 0.441 0.017
Litter weight at weaning, kg 63.89 ± 1.88 68.75 ± 1.88 63.86 ± 1.85 71.90 ± 1.56 0.405 <0.001
ADG b, kg/ litter/ day 1.74 ± 0.06 1.91 ± 0.06 1.73 ± 0.06 1.99 ± 0.05 0.531 <0.001
Weaning rate, % 93.09 ± 1.84 94.34 ± 1.99 91.56 ± 1.91 93.98 ± 1.38 0.588 0.288 a Gain= top 25 % of sows body weight changes Loss= last 25 % of body weight changes; Medium= sow body
weight changes between Gain and Loss b ADG= average daily gain
** No significant interaction between sow BW at weaning and BW changes during lactation
42
2.4 Discussion
Sows with heavy body weight at farrowing lost more body weight and P2 during
lactation than lighter body weight sows in the present study. This is accordance with
results reported by Quesnel et al. (2005b) and De Rensis et al. (2005). In our study, the
sows with the 25 % highest body weight loss during lactation were 11 kg heavier and
had 0.5 mm more backfat at the onset of lactation than the sows with 25 % lowest
body weight loss. Although heavier body weight at farrowing results in more body
reserves loss during lactation, the negative impact on the reproductive axis seems to
occur to a lesser extent in heavier lactating sows after weaning (Quesnel et al., 2005b).
A similar outcome was observed by Clowes et al. (2003b) and Quesnel et al. (2005b)
in experiments with protein restriction during lactation, and those authors
recommended that in primiparous sows a greater body weight at farrowing would
benefit post-weaning reproductive performance.
Sows that lost most body weight also had one more piglet at the start of lactation as
well as the end of lactation, compared to sows that lost least body weight. Overall, a
heavier body weight at farrowing and suckling of larger litters was accompanied with
greater litter ADG and more body weight loss during lactation. These data further
supports an association between maternal body mass at farrowing, requirements for
milk production, and body weight loss. Indeed, feed intake during lactation does not
meet the nutrient demands necessary for modern primiparous sows to rear large litters,
and therefore mobilisation of body mass must occur (Quesnel and Prunier, 1995) to
support milk production.
43
Sows that were lighter at weaning were also lighter at the start of lactation. However,
within the sows that were lighter than average at weaning (Table 2, model 2), there
was still a considerable number of sows with a more than average (-3.15 kg) body
weight loss during lactation. The average loss was -11 kg in the sub-group, and
indicates that even sows with relatively less body reserves at farrowing can still lose
considerable body weight during lactation. In fact, in the light group there were
relatively more sows (P = 0.06) with an above average body weight loss (56/100)
compared to the heavy group (36/85).
Excess body weight loss during lactation may compromise ovarian function (Clowes et
al., 2003b) and reproductive performance after weaning (Quesnel et al., 2005b). There
is also some indication that an increased protein mass at weaning reduces some of the
effects of body weight loss on reproduction (Quesnel et al., 2005b). However, WAI
and subsequent litter size were not affected by body weight change during lactation,
nor by body weight at weaning; there was no evident association with any body weight
variables in our study. In both models used in our study, the sows that lost more than
average body weight during lactation lost only about 6 - 7 % of their initial body mass
at the onset of lactation (on average). The present study is consistent with previous
findings (Thaker and Bilkei, 2005) that the weaning-to-service interval is not impaired
when body weight loss is below a 10 % threshold during lactation in first-litter sows.
Moreover, an absolute backfat depth at weaning (> 15 mm) has been recommended for
preventing post weaning infertility (Hughes et al., 2010). In contrast, De Rensis et al.
(2005) suggested that achieving a high pregnancy rate depends on the amount of
backfat loss (< 3 mm) during lactation, regardless of the amount of P2 at weaning. The
body reserves and body reserve change variables in our study did not exceed the values
44
recommended by the above authors, and our study was consistent with those earlier
findings in that we found no relationship between body weight or P2 variables and
WAI or subsequent litter size.
Average number of total born in the present study was 10.4 per litter which is lower
than the average for the Australian pig industry (11.1 per litter in primiparous sows;
Australian Pork Ltd, 2012), and clearly, the (small) litter size allocated to the sows in
this study did not pose a metabolic challenge sufficient enough to impact on
reproductive performance. Considering the strong relationship between litter size and
body weight loss in the current study, allocating larger litters (larger than 10) would
have incurred more body reserve mobilisation and possibly impacted on reproductive
performance. In addition, our period of data collection was during winter in Australia,
which can be related to an increase in feed intake from the beginning of lactation
(post-farrowing) and resulted in a lower body weight and P2 loss during lactation
(Prunier et al., 1996).
In conclusion, this study showed that the sows that lost most body weight during
lactation or had lowest body weight at weaning suffered no clear impact on post-
weaning reproductive performance. The modern primiparous sows may not be affected
in their post-weaning reproduction when rearing less than ten piglets during lactation,
as long as nutrient supply matches lactational requirement to minimize body weight
loss, and maintain adequate body reserves at weaning. Nevertheless, the relationship
between reproductive performance and metabolic challenges may vary with season,
and if the data in this study had been collected during summer, when feed intake is
limited, there may have been an impact on reproductive performance.
45
Chapter 3
Undernutrition during early follicle development
has irreversible effects on ovulation rate and
embryos
T.Y. ChenA, P. StottA, R.Z. AthornA, E.G. BouwmanB, and P. LangendijkB
ASchool of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy Campus, Roseworthy, South Australia, 5371.
BSouth Australian Research and Development Institute, Roseworthy Campus,
Roseworthy, South Australia, 5371.
Published in 2012 Journal of Reproduction, Fertility and Development (24) 886-892
46
Chapter 3
3.1 Introduction
In lactating first-litter sows, nutrient restriction during lactation results in excessive
mobilisation of maternal body reserves (Clowes et al., 2003a; Kim et al., 2004). As a
consequence, pulsatile release of LH may be reduced (Zak et al., 1997b) and the
weaning-to-oestrus interval prolonged (Yang et al., 2008). The reduced gonadotrophic
secretion affects both follicle recruitment during lactation (Kauffold et al., 2008) and
pre-ovulatory follicle development after weaning (Quesnel et al., 1998b; van den
Brand et al., 2000a). It is therefore presumed that insufficient energy intake during
lactation may reduce ovulation rate and embryo survival, because of impacts on
follicle development and, presumably, on follicle quality (van den Brand et al., 2000c;
Vinsky et al., 2006; Zak et al., 1997a).
In cyclic gilt models, it has also been shown that feed restriction during the luteal
phase has a negative effect on follicle development and ovulation rate (Hazeleger et
al., 2005), and subsequent embryo survival in early pregnancy (Almeida et al., 2000).
During the luteal phase in gilts the extent of follicle development is comparable to that
of sows in late lactation; follicle development is limited to small antral stages. Further-
more, with similar gilt models restricting feeding during the follicular phase, when
small antral follicles develop into large pre-ovulatory follicles, this impacts on follicle
development (Quesnel et al., 2000) and ovulation rate (Ashworth et al., 1999).
Following from the above, adequate nutrient supply during the early antral phase
(luteal phase of the oestrous cycle in gilts and late lactation in lactating sows), is
crucial to follicle development, follicle quality and ovulation rate, and can improve
47
embryonic survival in early pregnancy. However, there have not been any studies in
which the effects of nutritional planes during the early antral phase and the follicular
phase on folliculogenesis were studied together, and therefore the interaction between
nutrition planes during these two phases and any residual effects remain unclarified.
Such a scenario would allow the study of carry-over effects and compensatory follicle
growth during pre-mating oestrus. The aim of the present study was to use a gilt model
to evaluate the effects of different metabolic states during the pre-follicular (luteal)
phase and the follicular phase, and the interaction between these two phases, on
follicular recruitment and development, blood steroid concentration changes and
subsequent embryo development.
3.2 Methods
3.2.1 Experimental design
The experiment was conducted at the Pig and Poultry Production Institute (PPPI),
Roseworthy Campus, University of Adelaide. The study was approved by the animal
ethics committees of Primary Industries and Resources South Australia and the
University of Adelaide (Project No: S-2009-152). The experimental design was a 2 x 2
factorial arrangement in six replicates on a total of 47 crossbred gilts, with different
feed levels being applied during the luteal phase and the follicular phase of the pre-
mating oestrous cycle.
3.2.2 Animals, housing and feeding
Gilts were induced into puberty by a single intramuscular (i.m.) injection with 400 IU
of pregnant mare’s serum gonadotrophin and 200 IU of human chorionic
gonadotrophin (hCG) (PG 600; Intervet Pty Ltd, Bendigo East, Vic., Australia) at 24
48
weeks of age and 100 kg average bodyweight to induce their first oestrus. They were
housed in pens until they were transferred to individual stalls (2.23 x 0.61 m) in an
environmentally-controlled room before onset of their second oestrus. At 12 days after
their second ovulation, gilts were injected with Cloprostenol (Juramate; Jurox Pty Ltd,
Rutherford, Vic., Australia; two injections of 500 mg i.m. at 12 h intervals) to induce
luteolysis, and to provide a defined end to the luteal phase and the onset of the third
follicular phase. Gilts received 2 kg of a standard commercial diet (Table 3.1) daily
from the day of receiving PG 600 until the second ovulation. The trial commenced one
day after the second ovulation, and during the experiment, feed allowance followed the
experimental treatment.
3.2.3 Treatments
Gilts were then allocated to one of four treatments in a 2 x 2 design (HH, HL, LH and
LL) on the day of second ovulation, according to their body weight and ensuring the
four treatments all had similar average bodyweight (115.9 ± 1 kg; P > 0.05) at the start
of the treatments. Feed allowance was manipulated according to daily requirement for
maintenance (M). HH gilts received a high (1 M + 1.5 kg, 2.7 kg on average) and LL
gilts a low (1 M, 1.2 kg on average) feed level during the luteal phase following the
second ovulation and throughout the follicular phase preceding the third ovulation. HL
and LH received a high and a low feed level during the (second) luteal phase,
respectively, and were then re-allocated to a low, or a high feed level, respectively, on
the day after induction of luteolysis (Day 13 of the second cycle). Daily maintenance
requirement was calculated as M = [body weight 0.75 x 0.46] / 13.2 kg, with 13.2 MJ
DE/kg being the energy density of the diet), and M was calculated by actual body
weight of individual gilts. One day after the third ovulation (Day 0) until Day 8 of
49
early gestation, all gilts were provided the same feeding level: 1.8M, based on the
bodyweight at the day of third ovulation. For the duration of the treatments, orts were
collected from each feeder before the gilts received their morning feed. The same feed
was provided throughout the study period, and the composition and nutritional analysis
of the feed is shown in Table 3.1.
3.2.4 Oestrus detection and insemination
From one day after receiving Cloprostenol, oestrus detection was performed once daily
in the morning using fence-line boar contact with back pressure testing. Twice daily
oestrus detection commenced from four days after Cloprostenol and was maintained
until standing oestrus was no longer observed, in order to define the duration of
oestrus. Artificial inseminations (AIs) were given (with 3 x 109
spermatozoa from
pooled semen) at the first observation of standing oestrus and repeated every 24 h until
ovulation was determined.
50
Table 3.1 Composition of experiment diets (as fed basis)
Item % Ingredients Barley, 8.5 % 10.00 Wheat, 10 % 47.79
Millrun, 16 % 21.87 Peas 10.00 Canola expeller se 2.83 Meat meal, 55 % 3.90 Tallow 0.50 Salt 0.25 Limestone 1.25 Lysine-Sulphate 65 % 0.37 Choline Chloride, 75 % 0.04 Mono Dicalcium Phosph 0.70 L-Threonine 0.11 Alimet 0.05 Biofix Select 0.10 Breeder + Bioplex PMX 0.25 Analysed content DE (MJ/kg) 13.20 CP 15.02 Lysine 0.84 Fat 3.40 Fibre 4.64 Meth 0.25 Ca 0.90 Available Phosphorus 0.40
3.2.5 Measurements and observations
Bodyweights were recorded on the day of the second ovulation, Day 12 after the
second ovulation (end of luteal phase) and the day of the third ovulation. During the
pre-follicular phase, ovarian status was assessed once every two days in the morning
using transcutaneous ultrasound from Day 8 after the second ovulation. Follicle
diameter was measured using an ultrasonic device with 5 MHz sector probe (Aquila
Pro Vet. Esaote Europe B.V., Maastricht, The Netherlands). The ultrasound device
was equipped with cine-loop which enabled the recording of a 10 second clip, which
51
could then be scrolled through to identify the largest follicles on an ovary. From Day
13 (one day after the Cloprostenol injection), ultrasound scanning was performed once
daily in the morning until first standing oestrus was observed. Then, scanning was
performed every 12 h (morning and night) from the first day of standing oestrus until
the third ovulation. During the pre-follicular and follicular phases, the diameters of the
three largest follicles from one ovary were recorded and averaged to evaluate the
effects of treatment on follicle development. This method has been reported previously
by Soede et al. (2007) and Gerritsen et al. (2008). During the follicular phase, one
ovary may have five to roughly 25 follicles that can be considered part of the pool of
selected or dominant follicles, depending on the stage of the follicular phase. During
the luteal phase the pool of antral follicles is considerably larger. However, the method
used here assumes that the largest follicles are always representative of the most
advanced follicles. The largest (three) follicles will not represent a cross-section of all
antral follicles (except during the pre-ovulatory stage), but this study aimed at mapping
the most advanced follicles as a reflection of the stage of ovarian follicle development
at any given time. The durations of the intervals from the day of receiving
Cloprostenol to the onset of the third oestrus and to ovulation were recorded. Time of
ovulation was defined retrospectively as being 6 h before the scan at which the pre-
ovulatory follicles were no longer visible.
Blood samples were collected for analysis of gonadal steroid concentrations (oestradiol
and progesterone). Pre-prandial blood samples to assess oestradiol content were
collected by jugular venipuncture in the morning 3 days and 4 days after the
Cloprostenol injection. After ovulation, four blood samples were taken from each gilt
at 30, 54, 78, and 102 h to assess progesterone content. Blood samples were
52
immediately placed on ice after collection and centrifuged at 1300 g for 25 min at 4°C
before being stored at -20°C until they were analysed.
Oestradiol was assayed in 200 μL plasma by double-antibody radio-immunoassay
(RIA) according to the manufacturer’s instructions (Immunotech/Beckman Coulter,
Prague, Czech Republic). The sensitivity of the assay based upon the lowest standards
supplied with the two kits used was 4.5-5.5 pg/mL. Concentrations falling below the
assay sensitivity were assigned these values for statistical purposes. The intra-assay
coefficient of variation (CV) was < 10 % and the quality control samples supplied with
the kits were within the acceptable range. Plasma progesterone was determined in 50
μL of a 1 : 10 dilution of plasma in duplicate by double-antibody RIA according to the
manufacturer’s instructions (Beckman Coulter, Brea, CA, USA). The intra-assay CV
was always less than 10 %. The inter-assay CV was 9.6 % at 40 pg/tube; 4.9 % at 402
pg/tube and 11.5 % at 654 pg/tube. The limit of detection was < 1 ng/mL when using 1
: 10 diluted samples.
Gilts were slaughtered in the morning at a local abattoir on Day 9 or Day 9.5 after the
third ovulation. Ovaries and uteri were identified to the individual gilts. Corpora lutea
(CLs) were excised from both ovaries and counted to determine the ovulation rate, and
individual CLs were also weighed. Embryo collection was undertaken by flushing each
uterus with phosphate-buffered saline in a standardised manner, and embryo
dimensions were measured under a dissecting microscope. The ovulation rate was
determined by the number of CLs, and the embryo recovery rate was calculated as a
percentage by dividing the number of embryos after flushing by the total number of
CLs. It was assumed that embryo recovery is almost similar to embryo survival, even
53
though size of embryos may not be indicative of their survival. The total recovery rate
was determined as a percentage by dividing the number of embryos plus the number of
oocytes (if any) after flushing by the total number of CLs.
3.2.6 Calculations and statistical analyses
Characteristics recorded during the luteal phase were analysed using a univariate
model in PROC GLM: Y = μ + FLlut + e, where Y = dependent variable, μ = overall
mean, FLlut = feeding level during luteal phase and e = residual error. Characteristics
measured after the luteal phase (bodyweight changes during the follicular phase,
follicle size, oestradiol concentration, the intervals of luteolysis to oestrus and
luteolysis to ovulation, number, total weight and average weight of corpora lutea, as
well as number of embryos, embryo survival, recovery and dimensions), were analysed
with the following model in PROC GLM: Y = μ + FLlut + FLfol + FLlut x FLfol + e,
where Y = dependent variable, μ = overall mean, FLlut = feeding level during luteal
phase, FLfol = feeding level during follicular phase and e = residual error. The
interaction was not significant for any of the variables and was subsequently omitted
from the model. Plasma oestradiol concentrations on Day 3 were below the detection
limit (4.5 pg/mL) for some gilts and were nominally included for these gilts as 2
pg/mL. No interaction (FLlut x FLfol) was found between feeding levels during the
luteal phase and the follicular phase when an interaction test was included in the
model. Plasma progesterone data were analysed with the following nested model: Y μ
+ FLlut + FLfol + sow (FLlut x FLfol) + FLlut x FLfol + d + OR + e, where Y = dependent
variable; μ = overall mean; FLlut = feeding level during luteal phase; FLfol = feeding
level during follicular phase; FLlut x FLfol = interaction between feeding levels during
luteal phase and follicular phase; d = day; OR = ovulation rat; e = residual error. The
54
relevant co-variables and their interactions among treatments were also included in the
models above. All statistical analyses were performed with SAS (Edition 9.3; SAS
Institute Inc., Cary, NC, USA). The results are presented as mean ± s.e.m.
3.3 Results
The results for embryo characteristics only included the gilts (n = 40) that were
slaughtered between Day 9 and Day 9.5 after the third ovulation (Table 3.2).
Bodyweight changes during the different treatment periods, luteal phase (P < 0.05) and
follicular phase (P < 0.05), were influenced by feed level, as anticipated (Table 3.2).
The high feed level increased the follicle diameter of the largest follicles during the
luteal phase (Fig. 3.1), with the gilts on the low feed level achieving a mean diameter
of 3.0 mm at the last day of the luteal phase and gilts on the high feed level achieving a
mean diameter of 3.3 mm. During the early period of the subsequent follicular phase
(Days 1 and 2), gilts that were previously fed a high feed level during the luteal phase
still had larger follicles than those fed a low feed level, regardless of the feed levels
during the follicular phase.
During the follicular phase, gilts on the high feed level demonstrated a greater growth
rate of their follicles than gilts on the low feed level, regardless of the feed level during
the luteal phase, resulting in the mean follicle diameter at Day 5 of the follicular phase
being 6.9 mm and 7.0 mm for the LH and HH gilts, and 6.0 mm and 6.4 mm for the
LL and HL gilts, respectively. Despite the increased follicle growth rate during the
follicular phase on the high feed level, the feed level during the luteal phase had a
remnant effect on other ovarian characteristics (Table 3.2). The high feed level during
the luteal phase increased ovulation rate (14.4 vs 13.2) and shortened the interval from
55
luteolysis to the follicular phase did not influence these characteristics. Similarly, the
number of embryos at Day 9 of gestation was greater for gilts fed a high feed level
during the luteal phase, and this was not compensated for by the feed level during the
follicular phase. However, the interval from luteolysis to the onset of oestrus was
influenced by feed levels in both the luteal phase and the follicular phase. The
percentage embryo survival and recovery seemed to be higher for gilts on the high
feeding level during luteal phase; unexpectedly, there were no significant differences
between treatments for either survival or recovery in the present study. (P > 0.05;
Table 3.2).
56
Table 3.2 Gilt body weight changes and reproductive traits
Treatment a LL HL LH HH P- Values b L F
No. of gilts (n = 47) 12 12 12 11 Body weight Initial, kg 115.9 ± 2.1 115.0 ± 2.1 113.5 ± 2.4 116.2 ± 2.6 > .05 - During Luteal phase, kg/day-1 -0.1 ± 0.1 0.9 ± 0.1 0.0 ± 0.1 0.8 ± 0.1 < .001 - During Follicular phase, kg/ day-1 0.3 ± 0.1 -0.2 ± 0.1 1.3 ± 0.1 0.5 ± 0.1 < .001 < .001 Ovarian function Luteolysis-to-oestrus, day-1 5.9 ± 0.1 5.6 ± 0.2 5.8 ± 0.1 4.9 ± 0.1 0.005 0.045 Luteolysis-to-ovulation, day-1 7.2 ± 0.1 6.8 ± 0.2 7.0 ± 0.1 6.3 ± 0.1 0.004 0.101 Number of corpora lutea 13.1 ± 0.3 14.0 ± 0.5 13.3 ± 0.7 14.8 ± 0.5 0.048 0.373 Total weight of corpora lutea, g/ pig 5.95 ± 0.49 6.63 ± 0.35 6.47 ± 0.53 6.59 ± 0.59 0.420 0.628 Average weight of corpora lutea, g/ CL 0.45 ± 0.03 0.47 ± 0.02 0.48 ± 0.02 0.44 ± 0.03 0.844 0.957
Embryo characteristicsc No. of gilts (n = 40) 10 12 9 9 Number of embryos 11.1 ± 0.8 12.0 ± 0.6 10.0 ± 0.9 13.3 ± 0.6 0.013 0.448 Embryo survival, % 85.1 ± 6.1 86.3 ± 3.8 82.4 ± 9.6 91.9 ± 4.5 0.203 0.346 Embryo recovery, % 85.9 ± 6.1 89.6 ± 3.7 85.8 ± 7.5 93.8 ± 2.8 0.157 0.339 Embryo dimension, mm2 3.71 ± 0.70 2.70 ± 0.55 3.24 ± 0.57 3.11 ± 0.59 0.683 0.777 a LL = 1 M feed level during luteal and follicular phase; HH = 1 M + 1.5 kg feed level during luteal and follicular phase; LH = 1 M feed
level during luteal phase and then 1 M + 1.5 kg feed level during follicular phase; HL = 1 M + 1.5 kg feed level during luteal phase and
then 1 M feed level during follicular phase. b L= luteal phase effect; F = follicular phase effect. c Gilts were slaughtered between day 9 and day 9.5 after third ovulation.
57
Oestradiol followed the same pattern as follicle growth during the follicular phase,
with gilts on the high feed level during the follicular phase having a higher
concentration on Day 3 (P < 0.05) and Day 4 (P < 0.05). On Day 3 of the follicular
phase, all eight HH and all nine LH gilts had detectable (> 4.5 pg/mL) oestradiol
levels, whereas only five of nine HL and 8 of 11 LL gilts had detectable levels (Fig.
3.2). When gilts with non-detectable oestradiol levels were (arbitrarily) included in the
data analysis at 2 pg/mL, the average oestradiol level was 13.0 ± 1.9 pg/mL for HH
gilts, 10.7 ± 0.9 pg/mL for LH gilts, 7.9 ± 2.0 pg/mL for HL gilts and 7.9 ± 1.4 pg/mL
for LL gilts. On Day 4 there were only two gilts (one HL and one LH) with
undetectable oestradiol concentrations; these gilts otherwise had normal oestrus,
ovulation and fertilisation. Oestradiol on Day 4 was 15.2 ± 1.2 pg/mL for HH gilts,
14.5 ± 2.2 pg/mL for LH gilts, 10.4 ± 1.8 pg/mL for HL gilts and 10.3 ± 1.8 pg/mL for
LL gilts. The feed level during the luteal phase did not affect oestradiol levels (Fig.
3.2).
During the first four-day period after ovulation, plasma progesterone concentration in
all four treatments increased linearly (Fig. 3.3), and was related to ovulation rate (P <
0.05). There was an interaction between feed levels during the luteal and the follicular
phases. Progesterone concentrations did not differ between HH, HL and LH
treatments, but progesterone in the LL treatment was lower (P < 0.05).
In this study, there was no correlation between follicle diameter at the end of the luteal
phase (d -1) or at Day 1 or 3 of the follicular phase and the length of the follicular
phase (interval from luteolysis to ovulation). There was also no correlation between
follicle size during the follicular phase and oestradiol concentration. The follicle size at
58
the end of luteal phase or at ovulation (6 h before ovulation) was not related to
ovulation rate and embryo survival.
Ovulation rate was correlated with luteal mass (r = 0.48; P < 0.05) and progesterone
concentration at Day 2 (r = 0.33; P < 0.05) and Day 3 (r = 0.35; P < 0.05). There was,
however, no relationship between luteal mass and progesterone. Plasma progesterone
level was not related to the number of embryos at Day 9 of pregnancy. The number of
embryos was limited by the ovulation rate with a clear relationship between these two
characteristics (r = 0.58; P < 0.05), and with ovulation rate setting the maximum
number of embryos.
59
a)
b)
Figure 3.1 Follicle diameter as determined using transcutaneous ultrasonography from
(a) five days before luteolysis (d 0) to (b) the subsequent ovulation. HH
and LL were fed a high (1 M + 1.5 kg) and a low (1 M) feed level during
the luteal phase and follicular phase. HL and LH received a high and a low
feed level during the luteal phase and during the follicular phase were then
switched to a low, or a high feed level. Ovu = 6 h before ovulation. * P <
0.05, ** P < 0.005.
60
Figure 3.2 Plasma oestradiol concentrations for individual gilts on day 3 and day 4
after luteolysis (Day 0) in the four treatments. Some gilts in the HL and LL
treatments had oestradiol levels below the detection limit (4.5 pg/mL) on
day 3; these are (arbitrarily) represented at 2 pg/ml. Oestradiol
concentrations on day 3 (including concentrations < 4.5 pg/mL samples)
were influenced by feeding level during the follicular phase (P < 0.05).
The two gilts on day 4 with oestradiol below detection level (represented
as 2 pg/ml) otherwise had normal oestrus, ovulation, and fertilisation.
0
5
10
15
20
25
30
35
Pla
sma
oest
radi
ol(p
g/m
L)
Treatment
d3
d4
HH HLLH LL
61
Figure 3.3 Plasma progesterone concentrations at 30 h, 54 h, 78 h and 102 h after
ovulation (0 h) in the four treatments. Values differed between LH and LL
(P < 0.05).
3.4 Discussion
This is the first study that reports carry-over detrimental effects from the luteal phase
to the follicular phase by using a 2 x 2 factorial design, and that shows that these
effects may not always be fully compensated for by a high feed level during the
follicular phase. In this study, feed restriction clearly depressed body weight gain and
also reflected on follicle development in both the luteal and follicular phase. Gilts fed
the low feed level during the luteal phase had smaller follicles at the end of the luteal
phase and during the early follicular phase. However, as feed level was switched from
a low to a high feed level during the follicular phase, the gilts on the high feed level
had a higher follicle growth rate during this period than gilts that remained on the low
0
5
10
15
20
25
30
30 h 54 h 78 h 102 h
Pla
sma
prog
este
rone
(ng
/mL
)
Time relative to ovulation
HH
HL
LH
LL
HH
HL
LH
LL
62
feed level and similar to gilts fed the high feed level throughout. Despite the
compensatory follicle growth during the follicular phase, feed level during the luteal
phase had a remnant (carry-over) effect on follicle development, which was reflected
by a lower ovulation rate and a longer interval to ovulation in gilts that were restricted
during the luteal phase, regardless of their subsequent feed level. The effect of feed
level on early antral follicle development is consistent with Hazeleger et al. (2005)
who found in a gilt study that energy restriction during altrenogest treatment reduced
the number of larger follicles (> 4.5 mm) at the onset of the follicular phase and
ultimately reduced ovulation rate from 17.2 to 14.8. Using a gilt model Ashworth et al.
(1999) reported that gilts with a high feed level (3 M vs 1 M) before mating (entire
oestrous cycle) increased ovulation rate and embryo survival, but their study made no
distinction between the luteal and follicular phase. Almeida et al. (2000; 2001),
however, reported that feed restriction during the last week of the luteal phase did not
increase subsequent ovulation rate, but reduced progesterone and embryo. Quesnel et
al.(2000) found that a 0.8 M vs 2.4 M feed restriction during Days 3-12 of the oestrous
cycle (luteal phase) reduced the number of follicles at Day 13, whereas there was no
effect on LH; during this stage LH is still suppressed by progesterone, and may not
reflect nutritional interventions. Moreover, follicle development during this stage is not
yet dependent on LH secretion. Other nutritional cues, directly influencing ovarian
development, may impact on follicle development during this phase. For example,
Quesnel et al. (2000) reported that insulin and IGF-I were lower in feed-restricted gilts
and Almeida et al. (2001)reported that injections with insulin during the luteal phase in
feed-restricted gilts increased ovulation rate. Nevertheless, feed level during the
follicular phase does affect follicle growth, as reflected by the compensatory increase
63
in diameter of the largest follicles in gilts that were previously fed a low feed level in
this study.
Plane of nutrition during the follicular phase also affects follicle dynamics, but again,
previously this has only been studied separately from the luteal phase. Quesnel et al.
(2000) reported 20.6 vs 16.9 follicles with a diameter >5 mm at Day 19 of the cycle in
gilts that were fed 2.4 M vs 0.8 M from Day 14. In our study, gilts that were fed a high
feed level during the follicular phase had a faster increase in follicle size and also had
higher oestradiol levels, regardless of the feed level during the luteal phase. As pointed
out earlier, these effects on follicle development in the follicular phase did not
compensate for the loss in ovulation rate in gilts fed a low level during early antral
follicle development.
It remains unclear exactly which carry-over effects from the luteal phase impact on
subsequent reproductive performance. Undoubtedly, follicle dynamics are influenced
during the early antral stage and this is probably reflected in follicle numbers that are
recruited and selected and ultimately, numbers that ovulate. Follicle quality may also
be affected. Almeida et al. (2001) did not find an effect of luteal phase feed restriction
on the in vitro developmental competence of embryos recovered after ovulation, but
Ashworth et al. (1999) found a higher embryo survival and so did we, although not
significantly. Almeida et al. (2000) did report a higher progesterone level in gilts fed a
high feed level during the luteal phase, suggesting that an altered follicle quality
resulted in improved subsequent luteal function during early gestation. In our study
gilts fed a low feed level throughout also had a lower progesterone concentration after
subsequent ovulation.
64
Although the ovulation rate was correlated with luteal mass and progesterone
concentration, the absence of a correlation between luteal mass and progesterone
concentration was unexpected, because in a different gilt study in our group there was
a relationship between luteal mass and progesterone concentration (Athorn et al.,
2011). The reasons for this are unclear, as the concentration of progesterone is
dependent on the number of CLs as the source of secretion during early pregnancy.
Measurement of progesterone close to the site of secretion (e.g. in the vena cava)
rather than systemically, may have revealed a correlation.
Another possible explanation could be that the energy manipulation did not affect the
luteal mass but the quality of CLs was improved in gilts that had a high energy intake
during the luteal or follicular phase, resulting in no significant difference in
progesterone concentration between treatments except for the LL treatment. Possibly
the high feed level during the follicular phase in LH gilts allowed the previously feed-
restricted gilts to recover from catabolism with a high energy intake proceeding to
ovulation (Novak et al., 2003).
In comparable studies with primiparous lactating sows, Zak et al. (1997b) found that
well fed sows had larger follicles containing more mature oocytes than those whose
feed was restricted during late lactation (the final stages of oogenesis), and this
resulted in improved post-weaning follicle development. Van den Brand et al. (2000c)
reported that follicle size was more dependent on post-weaning LH pulsatility in sows
fed a low feed level during lactation and this was accompanied by a decreased
systemic insulin concentration, resulting in fewer follicles than in sows fed a high feed
level during lactation. A similar study by Zhou et al. (2010) suggested that elevated
65
energy intake during the rearing stage in pre-pubertal gilts improved oocyte quality,
due to the large follicles containing more follicular fluid with higher IGF-I and
oestradiol concentrations. IGF-I and oestradiol concentrations in follicular fluid have
been proven to be related to the proportion of oocyte maturation (Quesnel et al.,
1998b), and this indicates that feeding a high energy level during early antral follicle
development may result in a higher ovulation rate and a higher number of good quality
embryos, which is in agreement with our present study.
This experiment shows that energy intake during the luteal phase is crucial to
maximising reproductive performance in gilts. Although an increased energy intake
during the follicular phase can partially offset the detrimental effects on ovarian
function and gonadotrophic hormone secretion of energy deficiency during the luteal
phase, reproductive traits such as ovulation rate and number of embryos remain
compromised because of reduced follicle recruitment during that phase, which is when
early antral follicles are developing. The effects of feed restriction throughout the
oestrous cycle on follicle development can impact on luteal function after ovulation.
66
Chapter 4
Effects of pre-weaning substitutions on plasma
insulin and glucose profiles in primiparous sows
T. Y. ChenAB, P. StottA, S. O’LearyC, R. Z. AthornA, E. G. BouwmanB and P.
LangendijkAB
ASchool of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy
Campus, Roseworthy, SA, Australia
BSouth Australian Research and Development Institute, Roseworthy Campus, Roseworthy, SA, Australia
CDiscipline of Obstetrics and Gynaecology, The University of Adelaide, Adelaide, SA,
Australia
Published in 2012 Journal of Animal Physiology and Animal Nutrition DOI: 10.1111/j.1439-0396.2012.01321.x
67
Chapter 4
4.1 Introduction
Effects of feeding level on metabolic changes during lactation have been investigated
in many previous studies on primiparous sows. Energy intake during lactation, in
particular, has been shown to affect post-weaning reproductive performance, with a
number of studies showing the impact of feed restriction during lactation on either
ovulation rate or embryo survival or both (van den Brand et al., 2000c; Vinsky et al.,
2006; Zak et al., 1998). There are indications that besides the energy level, the energy
source during lactation can also affect post-weaning reproductive performance,
through LH secretion and insulin production (Koketsu et al., 1996a; van den Brand et
al., 2001). Insulin has been proposed as a hormone that acts as an intermediary
between nutrition and reproduction (Lucy, 2008). Endogenous insulin levels can be
influenced by the feeding level (Koketsu et al., 1996a) and dietary energy source
(Kemp et al., 1995) during lactation..
Several energy sources have been studied to improve the energy intake during lactation
in primiparous sows. Van den Brand et al. (van den Brand et al., 2000a) reported that
sows that were well fed or received a starch diet had greater concentrations of insulin
and glucose, accompanied by a greater number of LH pulses during late lactation.
Besides the effect of insulin and energy status on LH secretion, insulin also directly
acts on ovarian follicular development (Lucy, 2008). However, increasing the energy
density throughout the lactation may result in more milk energy output, associated
with more body weight loss, especially when starch is substituted by fat (van den
68
Brand et al., 2000b). A glucogenic supplement only during late lactation may not have
these negative effects on the energy balance.
Because feed intake in primiparous sows using a standard lactation diet limits the
energy intake level, we hypothesise that substituting part of the base diet with a
glucogenic diet during the last week of lactation, rather than during the whole lactation
period, would benefit ovarian function and reproductive performance after weaning.
Therefore, this experiment investigates different energy substitutions (fat or
carbohydrates) during late lactation and their effects on glucose and insulin profiles.
4.2 Materials and Methods
4.2.1 General experimental design
The experiment was conducted at the Pig and Poultry Production Institute (PPPI),
Roseworthy Campus, University of Adelaide, with the approval from the animal ethics
committees of Primary Industries and Resources South Australia and the University of
Adelaide (Project No: S-2010-108). The experiment comprised three treatments
(control, sugar and fat) testing the effects of nutritional substitutions during late
lactation on plasma insulin and glucose profiles.
4.2.2 Animals, housing and feeding
Primiparous sows (n = 21) were placed in the same environmentally controlled room
around 1 week before farrowing and were housed individually in a farrowing crate
until weaning. Litter sizes were standardised to 11 piglets by cross-fostering within 48
h of farrowing.
69
Sow body weight was recorded at 1 day after farrowing, at 9 days before weaning (day
of allocation) and at the day of weaning. Sows were fed 2 kg of a standard commercial
lactation diet (Table 4.1) from day 1 after farrowing, and the allowance was increased
by 0.5 kg/day until the maximum feed intake was reached. Each sow was fed to her
individual feed intake capacity as judged by refusals that were recorded on a daily
basis. At 9 days before weaning, sows were allocated to one of three treatments:
control (C), a fat-enriched substitution (F) or a sugar-enriched substitution (S). The
allocation was based on the individual average feed intake during the last 3 days before
allocation, to achieve similar mean intake across treatments. Feed was provided two
times per day (morning and afternoon) throughout the 28 day lactation period.
From allocation until weaning, each sow was provided the same amount of feed as
their individual feed intake at allocation for the remaining lactation period. The control
sows (n = 7) received their full allowance in the form of the lactation diet fed before
allocation. However, in the F treatment (n = 6), sows had 1 kg of the lactation diet
replaced by a fat-enriched substitute. Sows in the S treatment (n = 8) had 1 kg of the
lactation diet replaced by a sugar-enriched substitute (Table 4.1). The rationale was to
provide a feed allowance to the intake capacity of the individual sow, with the type of
substitution determining the predominant energy type (glucogenic vs lipogenic) and
the energy density of the total diet. Substitutions were provided at 500 g per meal with
little lactation diet to each sow to ensure the complete intake, than fed to the sows with
the rest amount of lactation diet each time. Sows had ad libitum access to water
throughout the lactation period. See Table 4.1 for the composition of the original
lactation diet and of the substitutions.
70
4.2.3 Observation and blood sampling
During the treatment period, serial blood samples were collected to determine glucose
and insulin profiles, 3 days before weaning. Sows were fixed by a snout rope for the
insertion of an ear vein catheter. A 1.5 mm PVC catheter (Microtube Extrusions,
NSW, Australia) was inserted 50 cm into a lateral or intermediate auricular vein in
each sow in C, F and S treatments before feeding in the morning, and blood samples
were collected on the same day. The exterior part of the catheter was secured in a
pouch at the back of the neck and taped by a Tensoplast Vet tape (BSN Medical,
Australia). For the sampling procedure, 1.5 kg of feed was provided (C sows: 1.5 kg of
lactation diet; F and S sows: 1 kg of lactation diet and 0.5 kg of substitute) in the
morning for all sows, to ensure they consumed the whole diet within two blood
samples after feeding.
Thirteen blood samples from each sow were collected at -24, -12, 0, 12, 24, 36, 48, 60,
72, 90, 132, 168, 204 min relative to feeding for the determination of glucose and
insulin profiles through the pre- and postprandial period. Blood samples were collected
in tubes containing 20 μl Heparin solution (5000 IU/ ml; Heparin Sodium BP, Pfizer
Pty Limited, Bentley, WA, Australia). Blood samples were immediately placed on ice
and centrifuged at 1300 g for 25 min at 4 °C. Plasma was stored at -20 °C until
analysed.
71
Table 4.1Composition of experiment diets (as fed basis)
Substitutions Items Sugar Fat Lactation diet Ingredients, % Barley, 9 % 20.18 Wheat extruded, 10 % 15.00 0.24 29.83 Choc biscuit meal 5.00 0.00
Millrun, 16 % 15.00 Peas 17.00 Soybean meal, 48 % 10.00 9.39 Soycomil 13.10 15.93 Canola expeller se 7.50 8.00 4.90 Full fat soya 2.50 - Meat meal, 50 % 5.25 7.31 Meat meal, 55 % 4.00 Fish meal, 55 % 5.00 5.00 Fish meal, 60 % 2.50 Vegetable oil - 46.00 4.00 Vege/Tallow blend 1.00 0.20 Salt 0.30 0.30 Limestone 1.05 Lysine HCL 0.05 - Lysine sulphate 65 % 0.30 Dextrose 10.0 - Sucrose 24.50 7.00 Sodium chloride 0.30 DL-Methionine 0.12 0.15 Di-Calcium phosphate 1.0 0.90 Phyzyme XP 5000 L 0.01 Alimet 0.05 Betaine liquid, 47 % 0.42 Betaine anhydrous 0.20 0.20 Breeder + Bioplex
PMX 0.25
Biofix 0.20 Tixosil silica 0.20 - Breed + Bioplex 0.25 0.25
Analysed content, % DE (MJ/kg) 15.75 23.85 14.10 CP 25.01 24.58 16.87 Fat 4.84 48.16 7.06 Starch 13.62 1.55 41.37 Fibre 4.78 Lysine 1.50 1.50 1.05 Meth 0.53 0.56 0.31 Ca 1.00 1.20 1.00 Available Phosphorus 0.55 0.63 0.49
72
4.2.4 Plasma analyses
Glucose was analysed by colorimetric automated analysis on a Hitachi 912 automated
centrifugal analyser with a commercial kit (Glucose HK assay kit, Roche Diagnostics,
NSW, Australia). Insulin was assayed in duplicate in 100 μL plasma using a specific
porcine RIA (pl-12K, Millipore, Billerica, USA). The intra- and inter-assay
coefficients of variation were less than 15 %. The minimum detection limit was 2 μU/
ml.
4.2.5 Calculations and statistical analyses
Mean glucose and insulin plasma levels were calculated for the period after feeding
(from 0 min to 204 min). Basal glucose and insulin levels were calculated from the
mean of three samples before feeding (from 24 min to 0 min). Peak glucose and insulin
levels were defined as the maximum value after feeding. Data for glucose and insulin
measurement, within each treatment group, were plotted, and the areas under the curve
(AUC) were calculated above basal glucose and insulin levels after feeding (from 0
min to 204 min).
Statistical analyses were all performed using SAS (9.3 edition; SAS Institute Inc, NC,
USA). Data recorded during the treatment period were analysed using a univariate
model in PROC GLM: Y = l + trt + e, where Y = dependent variable; l = overall mean;
trt = treatment (C, F and S) and e = residual error. Glucose and insulin profiles were
tested with sample time nested within sow, and statistical differences between
treatments were tested for each sampling time. The statistical significance of each
independent variable in the model was determined by using a significance level of P <
0.05. The results are presented as means ± s.e.m.
73
4.3 Results
At allocation (9 days before weaning), average body weight was 197.0 ± 7 kg, 200.0 ±
8 kg and 200.5 ± 6 kg for C, F and S respectively. During the treatment period, feed
intake averaged 5.0 ± 0.1 kg, 5.0 ± 0.1 kg and 4.6 ± 0.3 kg respectively. The different
substitutions did not affect body weight loss among treatments during late lactation
(11.5 ± 1.5, 9.1 ± 2.2 and 11.1 ± 1.1 kg for C, F and S sows; P > 0.05), and body
weight at weaning was similar (185.0 ± 7, 193.5 ± 8 and 189.5 ± 6 kg for C, F and S
sows respectively; P > 0.05).
Basal levels of plasma glucose did not differ among the C, F and S treatments (P >
0.05) and averaged 3.46 ± 0.18, 4.27 ± 0.25 and 3.74 ± 0.40 mM. After feeding, sows
in the S treatment had a greater glucose concentration at 24 min (6.74 ± 0.52 mM; P <
0.05) (Fig. 4.1) and reached the maximum concentration earlier at 36 min (8.14 ± 0.54
mM; P < 0.01), compared to C and F treatment sows that reached their peak plasma
glucose concentrations (7.03 ± 0.34 and 6.22 ± 0.29 mM) at 60 min and 72 min
respectively. The AUC was not significantly different among the C treatment sows
(483.72 ± 62.39 mM.min) and sows in F and S treatments (233.53 ± 39.99 mM.min
and 526.10 ± 135.81 mM.min).
Similar to plasma glucose patterns, the basal level of plasma insulin was not affected
by dietary treatments (C, F and S: 4.00 ± 0.53, 5.66 ± 1.04 and 5.20 ± 0.68 IU/ml; P >
0.05). However, the insulin concentration dramatically increased immediately after
feeding for sows fed the S diet, compared to the sows in the C and F treatment groups
(Fig. 4.2). The insulin level in the S treatment was higher (P < 0.05) at 24 min and
peaked at 48 min (207.43 ± 55.75 IU/ml; P < 0.05), compared to C and F treatment,
74
that peaked at 136.25 ± 28.40 and 72.25 ± 8.16 IU/ml at 60 min and 72 min. The AUC
was 9880.03 ± 2050.71, 6114.00 ± 1210.44 and 16168.50 ± 4938.50 IU min per ml (P
> 0.05) for the C, F and S treatments respectively.
Figure 4.1 Plasma glucose profiles for control (C, n = 7), fat (F, n = 6) and sugar (S, n
= 8) treatments during late lactation. abcTime points with different
superscripts/subscripts differ significantly (P < 0.05).
3
4
5
6
7
8
9
-24 0 24 48 72 96 120 144 168 192 216
Pla
sma
gluc
ose
(mM
)
Time relative to feeding (min)
C
F
S
aaaa
a
aabb
cb b b
b
ab
75
Figure 4.2 Plasma insulin profiles for control (C, n = 7), fat (F, n = 6) and sugar (S, n =
8) treatments during late lactation. abc Time points with different
superscripts/subscripts differ significantly (P < 0.05).
4.4 Discussion
Sows were fed approximately 33 % of the substitutions (0.5 kg substitutions + 1 kg
base diet) on the day of the glucose and insulin testing, which was at a higher density
of substitutions than what sows received on average (20 % of the substitutions on
average). This density of substitutions was chosen because a) sows that had low feed
intake (3.5 - 4.5 kg/day) were not able to finish their whole morning meal within 12
min after feeding, and b) the rate of substitution at sampling reflected the substitution
rate for sows with low feed intake, which are presumably most metabolically
challenged. These low feed intake animals were the target animals that we were
0
20
40
60
80
100
120
140
160
180
200
220
240
-24 0 24 48 72 96 120 144 168 192 216
Pla
sma
insu
lin
(μU
/ml)
Time related to feeding (min)
C
F
S
a
ba a
a
aa
a a
bbab
cb b b bc
76
interested in, because they would most likely have impacted reproductive performance
after weaning.
Circulating concentrations of glucose and insulin normally decrease as the lactation
progresses in sows (Koketsu et al., 1996b; Weldon et al., 1994). In previous studies,
low plasma concentrations of glucose and insulin were recorded after a 3 or 4 week
lactation. Yang et al. (2000b), for example, reported a decreased preprandial glucose
level of 3.03 mM and a preprandial insulin level of 6.04 IU/ml at weaning during a 3-
week lactation. Using a standard lactation diet, Mejia-Guadarrama et al. (2002)
reported preprandial glucose levels of around 3.33 mM and insulin levels of 7.77
IU/ml at the end of lactation, compared to preprandial levels of glucose around 5.00
mM and insulin around 12.80 IU/ml 1 day after weaning. These values are in
agreement with the observed preprandial levels in this study for glucose (3.46 mM)
and insulin (4.00 IU/ml) in C sows. An explanation for decreased blood glucose and
insulin concentrations is likely due to the mammary glands drawing on plasma glucose
for milk production (Spincer et al., 1969) as milk yield increases from the second week
of lactation (Quesnel et al., 2007).
The decline of insulin and glucose concentration during lactation is related to the
catabolic state and milk production, but is also influenced by the feed intake level and
energy sources. In primiparous sows that were fed 40 % of the diet given to control
animals throughout lactation, insulin (7.10 vs. 15.00 IU/ml) and glucose (4.16 vs 4.68
mM) were lower before weaning compared to high energy intake sows at 3 weeks of
lactation (Koketsu et al., 1996b). Similarly, Quesnel et al. (1998a) reported a lower
average insulin level (22.9 vs 48.3 IU/ml) in 50 % feed-restricted, lactating
77
primiparous sows. However, van den Brand et al. (2000a) did not find an effect when
there was a 25 % difference in the feed level on insulin and glucose profiles in
primiparous sows. Our study did not include feed level as a variable because the
individual intake capacity of the sows was regarded as a given, and therefore, energy
source was altered to manipulate postprandial glucose and insulin. As anticipated, the
postprandial profile of the plasma glucose and insulin concentrations for the sows that
had a sugar substituted diet increased immediately and resulted in a higher peak than
for F and C sows. The difference mainly reflected the difference between the diets
because prior to establishing the profiles, the sows were fed a standardised amount of
the diets. This finding is consistent with a previous study using a gilt model indicating
concentrations of glucose and insulin were raised immediately after feeding a sugar-
rich diet (van den Brand et al., 1998). In a later report, van den Brand et al. (2000a)
also found an increased postprandial glucose (mean 4.58 vs. 4.10 mM; peak around
6.66 vs. 5.00 mM) and insulin (mean 18.2 vs 15.2 IU/ml; peak around 32 vs 25 IU/ml)
in primiparous sows fed a starch-rich diet compared to sows fed a fat-rich diet during
lactation, but the diets were fed from farrowing throughout lactation. Furthermore, van
den Brand et al. (2000b) reported that sows that had fat-rich diets during lactation
drove more fat content into milk associated with facilitation of the mobilisation of a fat
tissue. As a consequence, sows in the fat-substituted group had a more negative energy
balance at weaning (Quiniou et al., 2008). It was for this reason, in the present study,
that the substitutions were only provided from 8 days before weaning, and sows were
fed at their voluntary feed intake capacity.
Eissen et al. (2003) suggested that an extra feed intake (about 4.8 kg/day) during
lactation in primiparous sows partly reduced body weight loss and backfat losses when
78
the sows were nursing large litters. In our study, sows that were fed the substitution,
however, had a similar intake (about 4.9 kg/day) but a higher energy density of the
total diet during the treatment period, especially those with a fat-rich substitution. An
accurate calculation of energy balance could not be established because litter weight
change was not recorded. However, body weight loss did not alter significantly
(although body weight loss was slightly lower for the F treatment), perhaps because
substitutions were only provided for a short period during lactation. This suggests that
the mobilisation of maternal body reserves was not influenced by energy sources, and
therefore, it can be assumed that the substitutions modified glucose and insulin profiles
without affecting the redistribution of body reserves into milk production. Milk
production, however, may have increased for sows with the fat substitution; this was
not recorded because this study focussed on maternal metabolism and not on litter
weight gain.
Providing a sugar substitution during late lactation clearly increases plasma glucose
and insulin concentrations in primiparous sows, without significantly affecting the
body reserve mobilisation. A further study is being performed to establish the impacts
on post-weaning follicle development, steroid hormones, reproductive characteristics
and also subsequent litter size, as insulin may directly or indirectly intermediate the
effects of nutrition on reproduction.
79
Chapter 5
Effects of pre-weaning energy substitutions on
post-weaning follicle development, steroid
hormones and subsequent litter size in
primiparous sows
T.Y. ChenAB, P. StottA, E.G. BouwmanB and P. LangendijkB
ASchool of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy Campus, Roseworthy, South Australia, 5371.
BSouth Australian Research and Development Institute, Roseworthy Campus,
Roseworthy, South Australia, 5371.
Published in 2012 Reproduction in Domestic Animals DOI:10.1111/rda.12118
80
Chapter 5
5.1 Introduction
Feed intake in primiparous lactating sows is generally insufficient to meet nutrient
requirements for milk production, with excessive mobilisation of body reserves as a
consequence (Dourmad et al., 1994; van den Brand et al., 2000a). Effects of feeding
level on metabolic changes during lactation have been investigated in restrict-fed sow
models, which show effects on either ovulation rate, embryo survival, or both (De
Rensis et al., 2005; Kirkwood et al., 1990; van den Brand et al., 2000c; Vinsky et al.,
2006; Zak et al., 1998).
Severe catabolism in lactating primiparous sows influences ovarian activity by
reducing post-weaning LH secretion (Clowes et al., 2003; Quesnel et al., 2007),
causing delays in ovarian follicle maturation and longer weaning-to-oestrus interval
(Yang et al., 2000a). Pre-weaning LH secretion is also reduced in sows with increased
catabolic state (Kirkwood et al., 1990; van den Brand et al., 2000a) and hence follicle
development may already be affected prior to weaning, with carry-over effects after
weaning.
In pigs in energy balance, some ovarian follicle development does occur during late
lactation, and following weaning, dominant follicles start to develop during the
follicular phase due to increased LH secretion (Soede et al., 2011; Zak et al., 1998).
However, Baidoo et al. (1992) demonstrated that even if sows are generously fed after
weaning, previous restriction during lactation still impacts on embryo survival. There
is evidence for lactational catabolism having effects on inherent follicle and oocyte
quality at weaning as well, compromising the number of follicles that develop after
81
weaning (Quesnel et al., 1998b) as well as their ability to undergo maturational
changes in vitro (Zak et al., 1997b). Similarly, feed restriction in cyclic gilts during the
period of early antral follicle development (during the luteal phase preceding the
follicular phase), has carry-over effects and reduces the number of antral follicles
(Hazeleger et al., 2005) and eventually ovulation rate and number of embryos (Chen et
al., 2012a).
As feed intake capacity limits energy intake in lactating primiparous sows, the dietary
energy source may provide a means to manipulate post-weaning reproductive
performance, through modulation of LH secretion and insulin production (Koketsu et
al., 1996a; van den Brand et al., 2001). Insulin has been proposed as a hormone that
acts as an intermediary between nutrition and reproduction (Lucy, 2008), both through
effects on gonadotrophins but also through direct effects on the ovary. Endogenous
insulin levels can be influenced by feeding level (Koketsu et al., 1996a), but also by
dietary energy source (Kemp et al., 1995) during lactation.
Increasing energy density of diets by varying the fat content, however, did not result in
any improvement of sow body condition during lactation and post-weaning
reproductive performance in studies by Heo et al. (2008) and Quiniou et al. (2008),
and actually aggravated the catabolic condition because of increased milk fat output
(van den Brand et al., 2000b). In contrast, increasing the carbohydrate content of the
diet throughout lactation, improved the energy balance and increased gonadotrophic
secretion, and insulin and glucose profiles. In a recent study, Wientjes et al. (2011)
found a positive correlation between post-weaning plasma insulin concentration and
82
progesterone level during early gestation in sows fed a carbohydrate-rich diet post-
weaning.
In previous studies with varied energy sources, the different lactation diets were fed
isocalorically throughout the whole of lactation. Hence, in the present study we tested
the effects of a fat- or carbohydrate-rich substitute fed non-isocalorically during late
lactation on post-weaning reproductive performance, peri- and post-ovulatory
endocrine characteristics and subsequent litter size, by boosting energy intake and/or
circulating glucose and insulin levels. We also included a post-weaning progesterone
treatment to serve as a positive control.
5.2 Materials and Methods
5.2.1 General experimental design
The experiment was conducted at the Pig and Poultry Production Institute (PPPI),
Roseworthy Campus, University of Adelaide, with approval from the animal ethics
committees of Primary Industries and Resources South Australia and the University of
Adelaide (Project No: S-2010-108). Four treatments (Control, Sugar, Fat and
Regumate) were studied to establish effects on post-weaning follicle development,
reproductive traits and subsequent litter size.
5.2.2 Animals, housing and feeding
Approximately one week before farrowing, primiparous Large White and Large White
x Landrace terminal line sows (n = 92) were placed in the same environmentally-
controlled room. Temperature was computer controlled and adjusted automatically
based on the day of lactation, with set temperature decreasing gradually from 24 °C
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approximately farrowing to 21 °C 14 days later. Piglets were provided with extra
heating using heating lights. During hot periods ventilation air was cooled by
evaporative cooling, which is effective in arid climates like in South Australian
summers. Litter sizes were standardised to 11 piglets by cross-fostering within 48 h
post-partum, and each litter was kept at 11 piglets throughout the lactation period.
Dead piglets were replaced by the same gender and similar body weight (difference
within 200g) piglets.
From farrowing (average BW 211.6 kg; P > 0.05), sows were fed 2 kg of a standard
commercial lactation diet as a basis but the feed allowance was stepped up by 0.5 kg
per day until maximum feed intake was reached. Feed refusals were weighed back and
recorded on a daily basis. Sows were assigned to one of four treatments at 9 days
before weaning. Average lactation length was 28 days, except for altrenogest treated
sows for which it was 21 days. Allocation to treatments was stratified based on the
average feed intake during the last three days before allocation and body weight (BW)
loss during the first three weeks of lactation (from one day after farrowing to one day
before start of treatments). Feed allowance during the treatment period was based on
the principle of paired-feeding, with sows in different treatments with similar feed
intake at allocation receiving equal feed allocation during the treatment period, except
for altrenogest-treated sows (see further). Feed was provided two times per day
(morning/afternoon) throughout the lactation period.
The four treatments were as follows. Control sows (negative control; C, n = 24)
received their full allowance in the form of the lactation diet. In the Sugar (S, n = 23)
and Fat (F, n = 23) treatments, sows received the same allowance in kilograms as their
84
pair-fed counterparts in the control treatment, but with 1 kg of the lactation diet
replaced by either a carbohydrate-rich substitution or fat-rich substitution respectively.
In the altrenogest treatment (positive control, R, n = 22) sows were weaned eight days
earlier than the other three treatments (one day after allocation), and fed a lactation diet
at 3.5 kg/day with one dose of altrenogest top-dressed twice a day on the morning and
afternoon feed (5 mL/dose containing 4 mg/mL of Regumate®, Intervet Australia Pty
Ltd, Bendigo East, MSD Animal Health, VIC, Australia) from one day before weaning
through to the day before the other sows were weaned.
The rationale of the altrenogest treatment was to provide a period of positive energy
balance in order to create a positive control in which early antral (pre-follicular phase)
development of follicles could occur during an anabolic state in order to improve
follicle quality and maximise ovulation rate after altrenogest withdrawal. The
altrenogest treatment coincided with the period of substitute feeding in the other
treatments to synchronise time of mating relative to farrowing between treatments and
separate effects of increased interval from farrowing to mating that are normally
associated with a post-weaning altrenogest treatment.
From the day of weaning or altrenogest withdrawal (start of the follicular phase and
resumption of the oestrous cycle) onwards, all sows received 3 kg/day of a gestation
diet (13.2 MJ/kg digestible energy; 15 % crude protein) until ovulation occurred. See
Table 5.1 for composition of the lactation diet and substitutions.
85
5.2.3 Oestrus detection and insemination
Starting from the day of weaning, sows had fence-line contact with boars for 15 min
daily in a heat detection and mating area. Twelve hours interval oestrus detection using
back-pressure testing was performed from Day 3 post-weaning or altrenogest
withdrawal until oestrus ceased. Sows were artificially inseminated (AI with 3 x 109
spermatozoa) with pooled semen at their first standing oestrus and this was repeated
every 24 h until ovulation was determined. Pooled terminal sire semen was ordered
and delivered at the same day in the morning from a local boar station and semen was
only used up to 48 h after collection. The same semen pool was used across treatments
in a given mating week. Weaning-to-oestrus interval was defined as the period
between weaning, or the morning after last altrenogest, and the time when a sow was
detected in heat for the first time.
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Table 5.1 Composition of experimental diets (as fed basis)
Substitutions Items Sugar Fat Lactation diet Ingredients, % Barley, 9 % 20.18 Wheat, 10 % 29.83 Wheat extruded, 10 % 15.00 0.24 Choc biscuit meal 5.00 0.00
Millrun, 16 % 15.00 Peas 17.00 Soybean meal, 48 % 10.00 9.39 Soycomil 13.10 15.93 Canola expeller se 7.50 8.00 4.90 Full fat soya 2.50 - Meat meal, 50 % 5.25 7.31 Meat meal, 55 % 4.00 Fish meal, 55 % 5.00 5.00 Fish meal, 60 % 2.50 Vegetable oil - 46.00 4.00 Vege/Tallow blend 1.00 0.20 Salt (Sodium chloride) 0.30 0.30 0.30 Limestone 1.05 Lysine HCL 0.05 - Lysine sulphate 65 % 0.30 Dextrose 10.0 - Sucrose 24.50 7.00 DL-Methionine 0.12 0.15 Di-Calcium phosphate 1.0 0.90 Phyzyme XP 5000 L 0.01 Alimet 0.05 Betaine liquid, 47 % 0.42 Betaine anhydrous 0.20 0.20 Breeder + Bioplex PMX 0.25 Biofix 0.20 Tixosil silica 0.20 - Breed + Bioplex 0.25 0.25
Analysed content, % DE (MJ/kg) 15.75 23.85 14.10 CP 25.01 24.58 16.87 Fat 4.84 48.16 7.06 Starch 13.62 1.55 41.37 Fibre 4.78 Lysine 1.50 1.50 1.05 Meth 0.53 0.56 0.31 Ca 1.00 1.20 1.00 Available Phosphorus 0.55 0.63 0.49
87
5.2.4 Measurements and observations
Sow body weight was recorded at one day after farrowing, nine days before weaning
(at allocation), and at the day of weaning. Follicle development was measured using an
ultrasonic device with 5 MHz frequency (Aquila Pro Vet. Esaote Europe B.V.,
Maastricht, The Netherlands). The ultrasound device was equipped with cine-loop
which enabled the recording of a 10 second clip which could then be scrolled through
to identify the largest follicles on one of the two ovaries. From the day of weaning,
scanning was performed transrectally once daily in the morning. Scanning was
performed every 12 h (morning/night) during oestrus and continued until ovulation.
The average follicle diameter of the three largest follicles from one ovary of each sow
was recorded to evaluate the effects of treatments on follicle development. The method
of measurement for follicle diameter has been described in a previous study (Chen et
al., 2012a). Time of ovulation was defined as when pre-ovulatory follicles were no
longer visible, minus 6 h. The duration of oestrus was defined as the first time sows
exhibited standing oestrus until the oestrus response was no longer exhibited. Sows
that failed to come into oestrus within 10 days were classed as anoestrous.
Blood samples were taken for evaluating the effects of treatments on steroid and
metabolic hormone concentrations. One pre-prandial blood sample was taken at one
day before weaning or altrenogest withdrawal for leptin assay, and one blood sample
was taken two days after weaning or altrenogest withdrawal, to assess the oestradiol
content. Two pre-prandial blood samples were taken at Day 2 (54 h) and Day 4 (102 h)
after estimated ovulation (Day 0) to assess the plasma progesterone content. Blood
samples were placed on ice and centrifuged at 1300 g for 25 min at 4 °C. Plasma was
stored at -20 °C until analysed.
88
Leptin was assayed in duplicate in 100 μl plasma using a Multi-Species leptin
radioimmunoassay (XL-85K; Millipore, Billerica, MA, USA). The cross-reactivity
with porcine leptin was 67 %. Results are presented as ng/ml HE (Human Equivalent).
The intra- and inter-assay coefficients of variation were less than 15 %. The minimum
detection limit was 1 ng/ml HE. Oestradiol was assayed in 200 μl plasma by double
antibody radio-immuno-assay (RIA) according to the manufacturer's instructions
(DSL-4800; Immunotech/Beckman Coulter, Prague, Czech Republic). The sensitivity
of the assay, based upon the lowest standards supplied with the 2 kits used, was 4.5 -
5.5 pg/mL. Concentrations falling below the assay sensitivity were assigned these
values for statistical purposes. The intra-assay coefficient of variation (CV) was < 10
% and the quality control samples supplied with the kits were within the acceptable
range. Plasma progesterone was determined by radioimmunoassay in 50 μl of a 1 : 10
dilution of plasma in duplicate by double antibody RIA according to the
manufacturer's instructions (IM1188; Beckman Coulter, Brea, CA, USA). The intra
assay CV was always less than 10 %. The inter assay CV was 9.6 % at 40 pg/tube; 4.9
% at 402 pg/tube and 11.5 % at 654 pg/tube. The limit of detection was < 1 ng/ml
when using 1 : 10 diluted samples.
Pregnancy was diagnosed using ultrasonography at four weeks after mating. Size of
the second litter (total born and born alive) and individual piglet birth weights were
recorded to determine the influence of treatments on the number of piglets born and
variation in individual birth weights within treatments. Subsequent litter size was
chosen for determining sow post-weaning fertility rather than early gestation because
lack of financial resources.
89
5.2.5 Calculations and statistical analyses
The statistical analyses were performed with the GLM procedure of SAS (9.3 edition;
SAS Institute Inc, Cary, NC, USA). Characteristics recorded during the treatment
period were analysed using a univariate model in PROC GLM: = μ + treatment + e,
where Y = dependent variable; μ = overall mean; treatment (C, F, S and R); e =
residual error. Statistical differences between treatments were tested for each
independent variable to assess effects on follicular dynamics, leptin and steroid
hormone concentrations, post-weaning reproductive performance and subsequent litter
weights. Covariates like BW loss were included in preliminary analysis and were
related to variables like weaning-to-oestrus interval, but did not affect significance of
treatments effects and were therefore excluded from further analysis.
Sows in C, F and S treatments were classified into three groups (across-treatments)
based on their body weight loss during lactation: body weight loss < 15 kg (n = 21),
intermediate body weight loss 15 – 30 kg (n = 34), and body weight loss > 30 kg (n =
15), to study the relationship between body weight loss during lactation and weaning-
to-oestrus interval or weaning-to-ovulation interval. Subsequent litter sizes were also
classified into 3 scores of number of total born piglets (excluding mummies) with
average piglet number <= 10, between 11-13 and > 13. Pregnancy rate and subsequent
litter sizes for the four treatments were compared using a non-parametric test.
5.3 Results
5.3.1 Sow performance
During the treatment period, sows in the R treatment lost less body weight than sows
in C, F and S treatments (P < 0.001) as they were weaned eight days earlier, but there
90
were no significant difference between sows in C, F and S treatments (Table 5.2). The
sugar substitution tended to reduce weaning-to-ovulation interval in S sows compared
to sows in C (P = 0.06) and F (P = 0.08) treatments, and tended to reduce oestrus
duration compared to sows in F treatment (P = 0.06). Sows in the R treatment had
longer intervals to oestrus and ovulation compared to other treatments.
Sows that lost < 15 kg body weight during lactation had shorter weaning-to-oestrus
(4.0 ± 0.1 days; P < 0.05) and weaning-to-ovulation (5.6 ± 0.1 days; P < 0.01)
intervals, compared to sows with intermediate body weight loss (4.60 ± 0.2 days and
6.14 ± 0.2 days) and sows with body weight loss > 30 kg (4.95 ± 0.2 days and 6.65 ±
0.2 days). Weaning-to-oestrus and weaning-to-ovulation intervals were both positively
correlated to body weight loss during week 1-3 (r = 0.29, P < 0.05; r = 0.35, P < 0.01),
during the treatment period (r = 0.28, P < 0.05; r = 0.29, P < 0.05) and total body
weight loss during lactation (r = 0.36, P < 0.01; r = 0.41, P < 0.001). However, no
correlation was found between body weight loss at any stages of lactation and
subsequent litter size.
Plasma leptin concentration at the end of the treatment period was higher in the R
treatment than in C, F and S treatments (P < 0.05). No anoestrous sows were observed
in this study. Pregnancy rate did not differ between the four treatments (Table 5.2).
91
Table 5.2 Sow body weight changes and reproductive traits during lactation
Treatment * C F S R P- Values
No. of sows (n=93) 24 23 23 22
Total feed intake, kg 125.9 ± 6.5 131.3 ± 5.6 127.9 ± 5.1 114.3 ± 5.6 > 0.05
Average feed intake during treatment, kg/day
5.0 ± 0.1 5.1 ± 0.1 5.1 ± 0.1 3.5 ± 0.1 > 0.05
Body weight, kg Day 1 after farrowing 213.1 ± 3.2 210.7 ± 4.3 210.1 ± 5.1 212.7 ± 4.2 > 0.05loss during treatments 10.9 ± 1.2a 10.6 ± 1.0a 10.6 ± 0.8a 1.3 ± 1.0b < 0.001loss during lactation 22.4 ± 2.7a 19.3 ± 2.3 a 21.5 ± 2.3a 10.6 ± 2.6b < 0.001
One day before weaning
Leptin, ng/mL 2.99 ± 0.19a 3.00 ± 0.20a 3.06± 0.24a 4.67 ± 0.39b 0.007Day 2 after weaning
Oestradiol, pg/mL 6.95 ± 0.64 7.78 ± 1.19 6.62 ± 0.52 8.07 ± 0.97 > 0.05
Reproductive traits weaning-to-oestrus, days 4.6 ± 0.3a 4.4 ± 0.1a 4.3 ± 0.1a 5.2 ± 0.1b 0.027weaning-to-ovulation, days 6.2 ± 0.2ax 6.2 ± 0.1ax 5.7 ± 0.1ay 7.0 ± 0.1b < 0.001Oestrus duration, hr 55.0 ± 2.8a 56.8 ± 1.8ax 49.5 ± 2.4ay 61.6 ± 2.5b 0.010Pregnancy rate, % 79 78 82 96 > 0.05
* C = commercial lactation diet; F = commercial lactation diet + fat substitution; S =
commercial lactation diet + sugar substitution; R = post-weaning altrenogest
treatment. The total feed allowance distribute equally among C, F, and S treatments. a,b Means without a common superscript letter differ (P < 0.05). x.y Means with different superscript tend to differ (P < 0.10).
5.3.2 Follicular development and plasma steroid hormone concentrations
On the day of weaning or altrenogest withdrawal, mean follicle diameter was similar
(P > 0.05) with an average of 3.7 ± 0.1 mm across the four treatments. During the
follicular phase, follicle size for sows in the R treatment tended to be smaller than C, F
and S treatments on Day 2 post-treatments (P = 0.08); however, follicle size did not
differ later during the follicular phase through to ovulation (Figure 5.1). Plasma
oestradiol concentrations did not differ between (P > 0.05) treatments at Day 2 of the
follicular phase (Table 5.2). Plasma progesterone concentration on Day 2 after
92
ovulation for sows with the sugar substitution was similar to sows in C and F treatment
(P > 0.05), but was higher than sows in the R treatment (P < 0.05). At four days after
ovulation, plasma progesterone concentration was greater for sows with the sugar
substitution (P < 0.05) than sows in C, F and R treatments (Figure 5.2).
Figure 5.1 Follicle diameter as determined using rectal ultrasonography from weaning
(Day 0) or altrenogest withdrawal to ovulation.
x,y Means without a common superscript letter tend to differ (P = 0.08).
0
1
2
3
4
5
6
7
8
Weaning day 2 day 4 Ovulation
Fol
licl
edi
amet
er(m
m)
Control
Fat
Sugar
Regumate
x x x y
93
Figure 5.2 Plasma progesterone concentrations at Day 2 and Day 4 after ovulation
(ovulation = Day 0) in the four treatments. Concentration at Day 4 was
significantly higher in S treatment (P < 0.05).
a, b indicates significance within the same day between treatments (P < 0.05).
5.3.3 Litter size and birth weights for the second litter
The data for the second litter size included 74 sows, 13 of which failed to establish
pregnancies (four sows in C, five sows in F, one sow in S and three in the R treatment
respectively), four sows aborted (three sows in C and one sows in the S treatment) and
one sow died during gestation in the R treatment. Overall, average numbers of total
born and born alive piglets were not influenced by treatments (P > 0.05; Table 5.3).
However, the average number of total born was significantly higher when only
compared between C and S treatments (P = 0.04). Moreover, classification according
02468
101214161820
Control Fat Sugar Regumate
Pla
sma
prog
este
rone
(ng/
mL
)
Treatment
day 2
day 4
a
a
bb
b
b
aa
94
to litter size showed that sows in the S and R treatments had a greater proportion of
litters with number of total born piglets in larger litter size classes (P < 0.05) : the
percentage of litters larger than 10 total born was 70%, 56%, 89% and 81% for C, F, S
and R. (Figure 5.3). The variation in birth weight (standard deviation) between piglets
did not differ among treatments (P > 0.05). Litter weights were similar across the four
treatments (P > 0.05).
Table 5.3 Effects of treatments on subsequent litter size
Treatment a C F S R P- Values
No. of sows (n=74)
17 18 21 18
Total born, n 10.7 ± 0.6* 11.4 ± 0.5 12.4 ± 0.5* 12.1 ± 0.4 > 0.05
Born alive, n 10.5 ± 0.6 11.0 ± 0.5 11.8 ± 0.5 11.6 ± 0.4 > 0.05
Birth weight, g 1637.3 ± 61.1 1579.1 ± 52.5 1582.1 ± 53.7 1592.82 ± 55.1 > 0.05
SD in birth weight 262.4 ± 23.1 269.4 ± 16.1 268.4 ± 21.1 278.7 ± 17.4 > 0.05a C = commercial lactation diet; F = commercial lactation diet + fat substitution; S =
commercial lactation diet + sugar substitution; R = post-weaning altrenogest treatment. b.When tested separately, S sows had more total born (P < 0.04) than C sows.
95
Figure 5.3 Subsequent litter size divided into three classes (number of total born <= 10,
11- 13 and > 13) and presented as percentage in the four treatments (P <
0.05).
* Significantly different from controls (P < 0.05).
5.4 Discussion
In the current study feed intake was not restricted but sows were fed to appetite.
Despite the absence of a purposely induced catabolic state, there was an effect of body
weight loss on reproductive performance, with sows that lost more weight having
extended weaning-to-oestrus and extended weaning-to-ovulation intervals. Litter size
however, was not related to body weight loss. Nevertheless, it can be postulated that
energy balance did have an effect on the reproductive axis. In the current study, feed
intake of the sows was considered as a given, and energy source was varied to
manipulate energy intake (the fat substitution specifically), but also glucose and insulin
profiles (sugar-rich substitution). Diets were not made isocaloric because the rationale
0102030405060708090
100
Control Fat Sugar Regumate
Lit
ter
size
prop
orti
on(%
)
Treatment
> 13
11 - 13
<= 10
* *
96
was that the volumetric intake capacity, and not the energy density of the diets, would
limit the energy intake. Studies by van den Brand et al. (2000b) and Park et al. (2008)
suggest that isocaloric substitution of the energy source in the diet with a fat source
throughout lactation may actually aggravate the negative energy balance by increasing
milk output and mobilisation of body reserves. Van den Brand et al. (2000b) showed
that replacing part of the energy source with starch had a positive effect on the energy
balance. Hence we hypothesised that providing energy substitutes during late lactation
could influence reproductive performance rather than feeding isocalorically.
The loss of similar amounts of body weight among Controls (C), Fat (F) and Sugar (S)
treatments during the last week of lactation indicated that mobilisation of body
reserves was not changed by altering energy intake via different energy substitutions.
Plasma leptin concentrations were also similar for control sows and those fed the
energy substitutes, suggesting similar fat reserves at the end of lactation because
circulating leptin concentration has been shown to be positively related to the status of
maternal body fat mass status (Estienne et al., 2000; Robert et al., 1998), and also
correlated with plasma insulin and luteinizing hormone (LH) concentrations between
well-fed and restricted-fed sows during lactation (Barb et al., 2008; 2001).
Furthermore, the higher energy intake in sows fed the fat-rich substitute may have
resulted in a higher milk output as shown in other studies (Park et al., 2010; van den
Brand et al., 2000c), but may not have resulted in a higher draw on body reserves as
reported earlier, due to a higher intake of energy.
The energy substitutes did have a clear effect on postprandial glucose and insulin
profiles, as we have reported in Chen et al. (2012b), and is in agreement with van den
97
Brand et al (2000a) who fed starch or fat-rich diets throughout lactation. Both glucose
and insulin reached higher levels after feeding the sugar-rich substitution, and were
lowest for sows fed the fat-rich substitution.
There is general agreement that metabolic intermediates such as glucose, insulin, and
IGF-I affect the reproductive axis both through their effects on gonadotrophic
secretion and through their direct effects on ovarian physiology, although these effects
may be independent (Lucy et al., 2001; Quesnel et al., 2000). Quesnel et al. (2000), for
example, showed that in a gilt model feed restriction in the pre-follicular (luteal) phase
does not necessarily reduce LH secretion but does affect ovarian follicular
development. In the same model these authors showed that suppression of LH with a
GnRH antagonist does also affect follicle development, stressing the importance of the
gonadotrophic axis and potential effects of a metabolic challenge. Studies using the
restricted feeding model in lactating primiparous sows have shown effects of a low
feeding level on glucose, insulin, and IGF-I (Quesnel et al., 1998a; Zak et al., 1997a),
on gonadotrophin secretion (Quesnel et al., 1998b; van den Brand et al., 2000a) and on
reproductive performance characteristics such as developmental potential of embryos
(Zak et al., 1997b), follicle pools (Quesnel et al., 1998b), weaning to oestrus and
ovulation rate (Zak et al., 1997a), and embryo survival (Zak et al., 1997b). However,
the evidence is not always consistent, with some modern primiparous sows showing
less impact of a metabolic challenge during lactation on the reproductive axis
(Patterson et al., 2011). Quesnel et al. (1998a) also pointed towards a correlation
between metabolic characteristics and LH secretion.
98
There is, however, less evidence of direct manipulation of glucose and insulin
homeostasis in lactating primiparous sow models having similar effects to restrict-fed
sow models. For example, van den Brand et al. (2000a) showed that a starch-rich diet
increased LH pulse frequency during lactation and improved follicle development, but
reported no effects on ovulation rate or embryo survival, although feed restriction did
have such effects. Van den Brand et al. (2001) reported an increase in IGF-I on a
starch rich diet and a correlation between IGF-I and LH secretion. Zhou et al. (2010)
reported an increase in in vitro developmental capacity of oocytes from gilts fed a
starch-rich diet as opposed to those fed a fat-rich diet during the luteal phase of the
cycle. Intravenous infusion with glucose (Tokach et al., 1992) did not immediately
increase LH secretion in primiparous lactating sows (however, in this study glucose
was infused for only one day); and insulin injection in primiparous sows (Quesnel and
Prunier, 1998) reduced milk production but did not seem to affect gonadotrophin
secretion, weaning-to-oestrus interval or ovulation rate. These authors did not study
insulin injection in non-restricted sows. In gilt models, insulin injection has been
reported to increase ovulation rate without affecting LH secretion or in vitro
developmental capacity of oocytes (Almeida et al., 2001), and Quesnel et al. (2000)
reported no effect of insulin.
Taken together, manipulation of glucose and insulin profiles in our study may have,
but not necessarily, increased LH secretion, and may also have had direct effects on
ovarian physiology through a stimulatory effect on follicle development with a larger
available pool of follicles at the start of the follicular phase at weaning, and possibly
effects on developmental potential of the ovulated oocytes. These factors would
explain the increased litter size in the sugar-rich supplement and altrenogest-treated
99
sows, although LH secretion and ovulation rate were not measured in our study. Size
of the largest follicles was monitored by ultrasound and did not show any difference
between the treatments, which is in agreement with Hazeleger et al. (2005) who
reported that follicle size during the early follicular phase was associated with feed
level during the pre-follicular phase, regardless of the energy sources (starch vs fat), in
a gilt model. This does not necessarily rule out an effect on the size of the follicle pool.
Actually, we did find that the sugar-rich substitution tended to reduce the weaning-to-
oestrus interval and ovulation duration, indicating effects on follicle dynamics. A
further study is required to elucidate effects of the manipulations on follicle quality
and ovulation rate.
Apart from the potential effects of treatments on glucose and insulin homeostasis and
on metabolic status in general, with related effects on follicle pool development and
inherent follicle and oocyte quality, the increase in litter size in the sows treated with
the sugar rich supplement or altrenogest may also have been caused by a reduced
embryo mortality due to an improved uterine environment. Similar to our results,
Kemp et al. (1995) reported a positive effect on the LH surge accompanied with higher
progesterone levels during early gestation in sows that were fed an insulin-stimulating
(starch) diet compared to sows fed a fat diet during lactation, although van den Brand
et al. (2000a) did not find such effects in a similar model. Wientjes et al. (2011)
reported a correlation between insulin concentrations in the post-weaning period and
progesterone levels after ovulation. The effects of diets on progesterone concentration
may be a combination of a higher ovulation rate, which can be correlated to a higher
progesterone output (Athorn et al., 2011), and to the secretory capacity of the
increased luteal tissue mass. In fact, Chen et al. (2012a) showed that in a gilt model a
100
low feeding level throughout the luteal and follicular phase preceding mating resulted
in a lower post-ovulatory progesterone increase compared to gilts fed a high feed level,
even after correction for ovulation rate.
A longer weaning-to-oestrus interval was observed in sows treated with altrenogest
following lactation. Oestrus may have been postponed because of the double dose of
daily altrenogest that was applied in our study. In a recent study (van Leeuwen et al.,
2011b), the pattern of LH secretion throughout the day after altrenogest administration
in the morning was suppressed for about half a day (average 0.3 pulses per 9 h
compared to 2.5 pulses in control sows), but pulsatile release increased thereafter. This
suggests that in our model, applying a second dose at the end of the day would have
suppressed LH release for a full 24 h period. Therefore, “normal” post-weaning LH
secretion could have been delayed after the last altrenogest administration in the
present study, and resulted in a delay of follicle growth compared to the other three
treatments. Nevertheless, litter size was increased in the altrenogest treated sows,
which is in agreement with a recent study by Patterson et al. (2008); however, our
study shows a positive effect of the altrenogest treatment in sows that were mated at a
similar time after altrenogest withdrawal compared to other treatments, uncoupling the
effects of uterine recovery.
In conclusion, both sugar- and fat-rich substitutions as dietary energy sources during
late lactation had no significant effects on sow body condition at weaning and post-
weaning reproductive performance, but circulating progesterone concentration and
subsequent litter size were improved in sows fed a sugar-rich substitution, and there
was a tendency towards a reduction in the weaning-to-ovulation interval that was not
101
matched in the sows fed a fat-rich substitution. Moreover, sows allowed to recover
metabolically by altrenogest treatment for a week following weaning also had larger
litters, indicating that manipulating the glucose and insulin homeostasis or a week of
metabolic recovery can improve reproductive performance in sows that are
metabolically challenged during lactation.
102
Chapter 6
General discussion
103
Chapter 6
6.1 Introduction
Reproductive performance is a major contributor to lifetime performance, since about
42 % of first litter sows are culled for reproductive reasons (Lucia et al., 2000). Lower
farrowing rates or suboptimal litter sizes are typical for the second parity (the so-called
second litter syndrome) (Hoving et al., 2010; Saito et al., 2010), and can have a
profound influence on litter sizes in subsequent parities (Hoving et al., 2011). It is
therefore important to improve reproductive performance in sows during their first
lactation in order to increase lifetime breeding efficiency and the average parity of
breeding herds, and also to reduce replacement costs in commercial farms.
This thesis has evaluated reproductive performance in relation to body weight change
during lactation in primiparous sows at their first weaning. The parameters were the
subsequent litter size and the physiological responses including follicular dynamics
and the concentrations of metabolic and gonadotrophic hormones following energy
manipulations pre-mating, during the luteal phase of the oestrous cycle, or during
lactation. The results from these studies are combined and discussed in this chapter and
practical recommendations will be given.
6.2 Body reserves mobilisation during lactation and the status at weaning
Post-weaning reproductive performance in primiparous sow is associated with sow
body reserve losses during lactation. Retrospective studies indicate that modern
primiparous sows have inadequate body backfat levels at farrowing and feed
consumption typically is insufficient during lactation, resulting in detrimental impacts
of the resulting catabolic status on follicular development, oocyte quality, weaning-to-
104
oestrus interval, ovulation rate, embryonic survival, and subsequent litter size (Chapter
1). In most previous studies on feed restriction (Table 1.1), feed regimes for the
restricted sows were often 50 % of the levels for the sows that had a high feed level in
order to provide a clear contrast, and for those restricted sows the catabolic state was
evident from the body weight loss during lactation. The reality in the commercial pig
industry is that lactating sows are generally fed ad libitum to encourage lactational
feed intake; nevertheless, post-weaning reproductive performances in primiparous
sows and their subsequent litter size are still similar or less than for the first litter
(Chapter 2). Clearly, the increased body weight loss in those lactating sows that have a
low voluntary feed intake during lactation causes a poor reproductive performance
outcome (Quesnel, 2005) and also increases the number of culls at first weaning
(Hughes et al., 2010).
Many scientific studies have addressed the issue of body reserve mobilisation during
lactation. Preventing sows from losing more than 10 % body weight during lactation
(Thaker and Bilkei, 2005) by increasing feed intake (Hoffmann and Bilkei, 2003) or
energy intake (van den Brand et al., 2000c)(Chapter 5; Table 6.1) can improve embryo
and/or subsequent litter size. On the other hand, sows that had more body reserves at
farrowing were more capable to cope with severe feed or lysine restriction and
weakened the association between post-weaning reproductive performance and body
weight loss during lactation (Quesnel et al., 2005a). The metabolic state in the heavier
sows could, at least in part, buffer the impacts of negative energy balances on post-
weaning reproductive performance (Quesnel et al., 2005b), in terms of the
responsiveness of the ovaries to increased LH secretion and metabolic hormone
concentrations. The data in Chapter 2 were collected from sows fed ad libitum in a
105
commercial farm in South Australia to provide a clear perspective of the current
circumstances applying in the pig industry regarding relationships between post-
weaning reproductive traits and body weight loss during lactation or body weight at
weaning in primiparous sows, and their effects on subsequent litter size. The body
weight loss and metabolic status at weaning and the effects on reproductive
performance were less pronounced in our study, which confirms the findings by
Thaker and Bilkei (2005), that as long as body weight loss is not over a 10 % threshold
during lactation, there is little impact on reproductive performance. Although no
influence on post-weaning reproductive performance between categories of sows with
different body weight loss or body weight at weaning was found in our study, 43 % of
the sows did not improve the number of piglets born in their second parity. Clearly,
body weight loss is not the only major factor that influences the size of the subsequent
litter in primiparous sows, and presumably, the progress of lactation also has an
influence on the regulation of reproductive and metabolic hormones and impacts on
post-weaning ovarian activation. A review by Quesnel (2009) demonstrated that
modern sows have been selected for shorter weaning-to-oestrus intervals. As a result,
the period between weaning and ovulation may be too short to recover from the
lactational burden, particularly in primiparous sows, therefore compromising ovarian
function by extending the impact of the negative energy balance during lactation on
follicular development and oocyte quality during the follicular phase. The reduction of
follicular development and oocyte quality can lead to low ovulation rates with low
circulating progesterone concentrations during early gestation, and eventually to lower
embryo survival (Vinsky et al., 2006; Zak et al., 1997a)(Chapter 3).
106
Table 6.1 Digestible energy intake during lactation in four treatments
Treatment * Control Fat Sugar Regumate
Average feed intake from farrowing to one day before treatment start, kg/day
4.2 4.4 4.4 4.3
DE MJ/day 59.2 61.9 61.3 60.8
Average feed intake during treatment, kg/day
5.0 5.1 5.1 3.5
DE MJ/day 70.5 81.7 73.6 49.4
6.3 Influence of pre- and post-weaning energy balance on ovarian function and
reproductive performance
Negative energy balance in relation to ovarian function and subsequent litter size has
been broadly studied. Energy restriction during lactation has been shown to reduce
either follicle development and ovulation rate or embryo survival, or both, in
primiparous sows (van den Brand et al., 2000a; Vinsky et al., 2006; Zak et al., 1998).
On the other hand, increasing post-weaning feed or energy intake has been
recommended in practical circumstances, which may improve sow performance by
shortening the weaning-to-oestrus interval (Boyd et al., 2002), or follicle development
via stimulation of LH (Quesnel et al., 2007). Similarly, gilt models have been used to
test the effects of energy manipulation in either the pre-follicular (luteal) phase
(Almeida et al., 2000; Hazeleger et al., 2005) or the follicular phase (Ashworth et al.,
1999; Quesnel et al., 2000) on follicle development and ovulation rate, and embryo
recovery. In those studies, the effects of energy intake on reproductive traits have only
focused on one part of the breeding cycle. However, each phase in the sow breeding
cycle is related and a restricted energy intake in one phase may have an influence on
the following phases; unfortunately, these interactions remain unclarified. Therefore,
107
in my study the interactions between energy intake during the pre-follicular and
follicular phase were separately investigated, using a cyclic gilt model, to study the
carry-over effects during the pre-mating period (Chapter 3). The findings clearly
indicate that the pre-follicular phase is a critical period and the metabolic status during
this period influences ovulation rate and number of embryos, and also progesterone
secretion during early pregnancy. The detrimental effects of feed restriction during the
luteal phase were not compensated by improved metabolic status during the
subsequent follicular phase. As the pre-follicular phase in gilts is comparable with
sows during lactation (in regards to the extent and dynamics of follicle development),
the findings in my study may explain why even though the metabolic status of sows
returns to anabolism before ovulation occurs, there may still be a residual effect of
energy restriction during lactation on ovarian activity, follicle development and oocyte
quality (Chapter 3).
6.4 Potential improvement for reproductive performance in primiparous sows
As lactation progresses, in primiparous sows, a negative energy balance results in an
accumulated energy deficit. The reduction in circulating insulin and Insulin like
Growth Factor (IGF-I) concentrations at weaning have been related to negative energy
balance at weaning, as well as follicle development, oocyte quality and reproductive
performance (Koketsu et al., 1996b; Quesnel et al., 2000; Zak et al., 1997a). Hoving et
al. (2012) suggest that IGF-I concentrations were negatively correlated with body
weight loss during lactation, and sows that had low body weight loss during the last ten
days before weaning had a higher average IGF-I concentration and number of
embryos. Indeed, insulin and IGF-I concentrations may mediate follicle development
either directly by affecting the responsiveness of ovaries to gonadotropins (Quesnel,
108
2009), or indirectly by improving the hypothalamus-pituitary-axis to amplify LH
pulsatility (Prunier and Quesnel, 2000a). Insulin and IGF-I can be manipulated by
increasing feed intake (Prunier and Quesnel, 2000b) or feed composition (insulin-
stimulating diet) (Kemp et al., 1995; van den Brand et al., 2001) during lactation.
Feed intake, particularly, has been reported to affect post-weaning reproductive
performance, but energy intake is limited due to feed intake capacity during lactation
in primiparous sows. Hence, since using a standard lactation diet limits energy intake
level, increasing the energy content of the diet level could be an option to improve sow
productivity via feeding an insulin-stimulating diet to increase plasma insulin levels
(Chapter 4). Increasing circulating glucose concentration has been reported to
positively influence LH secretion from the pituitary (Barb et al., 2001). Further, van
den Brand et al. (2000a) suggested that a carbohydrate rich diet stimulates follicle
development and oocyte quality, and this effect may be due to increasing LH secretion
and higher plasma insulin and IGF-I levels (van den Brand et al., 2001). This indicates
a substantial positive effect of an insulin-stimulating diet on subsequent litter size. In
my study (Chapter 4 and 5), a sugar rich diet was only provided during 8 days before
weaning rather than throughout the whole lactation period. The hypothesis for Chapter
4 and 5 was that the sugar-rich diet would benefit ovarian activity of lactating sows
more than improve piglets growth during lat lactation, as opposed to diets rich in fats.
In my pigs, the concentrations of circulating glucose and insulin were raised
immediately after feeding a sugar rich substitution but not following fat rich
substitution, however, sow body weight loss during the lactation and treatment period,
and post-weaning follicle development in treatments were not influenced by energy
sources (control, fat and sugar)(Chapter 4). Post-ovulatory progesterone concentration
109
in sows fed a sugar rich substitution was improved and these sows produced larger
litters than sows fed a fat rich substitution and standard lactation diet (Chapter 5).
Besides, in one treatment within the same experiment, sows treated post-weaning
using altrenogest to allow a week to recuperate from the negative energy balance
during lactation also had larger litters, suggesting that manipulating the glucose and
insulin homeostasis or a week of metabolic recovery can improve reproductive
performance in primiparous sows (Chapter 5).
6.5 Practical and future research recommendations
At the sow level, body weight loss should be minimised to around 10 % during
lactation to prevent any negative effects arising from catabolism during the first
lactation. This can be approached by using a step up feeding regime to encourage sows
to maximise their feed intake after farrowing, and reduce suckling load
(standardisation of litter size equal to or less than 10 piglets) in order to decrease the
excessive mobilisation of body reserves, particularly for primiparous sows that have
low appetites during lactation. Manipulating dietary energy intake during late lactation,
specifically, using an insulin-stimulating diet as a substitution or a fully formulated
lactation diet, can increase subsequent litter size in primiparous sows. Furthermore,
adjusting environmental conditions to reduce heat stress can also increase feed intake
in lactating sows in summer. Room temperature during farrowing should be higher
(around 30 °C) to avoid hypothermia in new born piglets (Black et al., 1993), but the
room temperature should then be steadily decreased to around 24 °C by the end of first
farrowing week. Ideally, providing an appropriate microclimate area in farrowing
crates for piglets can avoid a reduction of sow feed intake due to high room
temperature and also keep piglets in a warm environment. If such a microclimate is
110
provided, ambient temperature around farrowing can be reduced to 25 °C and drop to
20 °C one week later. Sufficient water supply is another important factor to influence
feed intake during lactation (Kruse et al., 2011). For maximise feed intake, well-
functioning water nipples and fresh cooling water should be freely accessible,
particularly during summer.
At the farm level, oral altrenogest administration can be a useful strategy for post-
weaning sow management. The recommendation of using altrengest in commercial
piggeries is to provide one dose daily; however, altrenogest treatment does not always
yield positive outcomes in practical circumstances. A study by van Leeuwen et al.
(2011a) failed to find any improvement on subsequent litter size. Hence, altrenogest
should be applied from one day before weaning to avoid gonadotropin increase
immediately after weaning, and the study in Chapter 5 suggests that it may be more
effective to give double doses of altrenogest daily for a week, in order to improve
reproductive performance and synchronise weaned sows to come into oestrus after
altrenogest withdrawal. Altrenogest administration may increase the non productive
days per sow per year and the cost of altrenogest, however, the extra piglets born at
following parity and also increasing of sow longevity would be able to cover the
additional expense.
This thesis provides some understanding as to the crucial period during lactation for
improving follicular development and reproductive performance by changing
endocrine profiles through energy manipulations during lactation in primiparous sows.
However, some critical aspects remain uncertain, particularly the detail of the
physiological mechanisms that link a sugar-rich diet with large subsequent litter size.
111
For example, it has been reported (van den Brand et al., 2000a; van den Brand et al.,
2001) that increasing insulin and IGF-I concentrations may have direct effects at the
ovarian level, and my results in Chapters 4 and 5 are consistent with those reports.
However IGF-I concentrations were not assayed in my studies, and it would be
interesting to include the relationship between IGF-I concentrations and ovarian
parameters in this thesis. The effect is possibly through an increase in the number of
available antral follicles in the pool at the start of the follicular phase, but another
effect may be an improvement in the quality of oocytes (Prunier and Quesnel, 2000a)
On the other hand, increased circulating glucose and insulin concentrations have been
reported to influence LH secretion (Koketsu et al., 1996b; van den Brand et al., 2000a)
and the pre-ovulatory LH surge (Kemp et al., 1995); thus, there may also be indirect
stimulatory effects on ovarian follicle development, resulting in high ovulation rates
with a subsequent but concomitant increases in circulating progesterone levels
accompanies increasing circulating progesterone level eventually. It would be
interesting to determine the actual mechanism affecting ovarian physiology by
increasing circulating glucose and insulin concentrations and whether there were direct
and/or indirect effects on ovarian physiology that were causing the large subsequent
litter sizes.
6.6 Conclusion
In summary, post-weaning reproductive performance in primiparous sows is
compromised by the quantity of body reserves mobilised during lactation, balanced
against restricted energy intake during that period. Achieving a high level of post-
weaning reproductive performance is a means of reducing the average number of non
reproductive days per sow per year and the number of young sows that are culled. This
112
improvement will result in an increase in sow longevity and lifetime reproductive
performance, which are parameters of reproductive efficiency in sow herds. Modern
prolific sows tend to be less affected by body weight loss during lactation, as long as
feed intake is maximised to minimise sow body weight loss during lactation (Chapter
2). Moreover, energy intake is one of the most important factors for lactating sows.
Our gilt model shows that a higher energy intake during the pre-follicular phase can
improve ovulation rate and the number of embryos, although increased energy intake
during the follicular phase may partially repair the detrimental effects on ovarian
function and gonadotrophic hormone secretion (Chapter 3). Similarly, increasing
energy intake during lactation may alleviate the negative energy balance and reduce
body weight loss. But more particularly, as shown in Chapter 4 and 5, manipulating
energy source by insulin stimulating substitution during late lactation positively
improved circulating progesterone concentration and litter size in second parity.
Moreover, altrenogest administration for a week after weaning for energy restoration
can positively affect subsequent litter size. The results in this thesis should contribute
to optimising guidelines for managing modern primiparous sows during lactation, and
may help improve reproductive performance and longevity in the pig industry.
113
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