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GWR 227206 Integrative Veterinary
Physiology
Integrative Veterinary Physiology
Ruminant Digestion
Dr G W Reynolds
Room 2.17 Riddett Building
Institute of Food Nutrition & Human Health
Extn. 7507
Email [email protected]
1
GWR 227206 Integrative Veterinary
Physiology
Herbivores
One of the most successful groups of
terrestrial animals
Their main energy source is plant structural
carbohydrates (cellulose, lignin).
Mammals do not produce cellulase
Herbivores have established a symbiotic
relationship with suitable microbes (produce
cellulase)
Specialised regions within the GI tract that
serve as large fermentation chambers.
In the odd toed ungulates e.g. the horse, this
fermentation chamber is a greatly enlarged
hindgut.
In ruminants there is an enlarged region
between the oesophagus and the gastric
stomach – the forestomach
[Latin ruminare means to chew again]
2
GWR 227206 Integrative Veterinary
Physiology
Advantages of Ruminants
The forestomach allows
ruminants to exploit as their
food source the most abundant
carbohydrate form on the
planet.
It allows ruminants to thrive in
niches where the quality of the
herbage is too low to support
nonruminants
For example above the Arctic
Circle (musk oxen), in high
mountains (llamas, yaks) and
in the hot deserts (camels,
goats).
3
GWR 227206 Integrative Veterinary
Physiology
Advantages of Ruminants
The microbes synthesis relatively
high quality proteins from
low quality plant proteins
non-protein nitrogen
recycled nitrogen-containing end
products of metabolism (e.g. urea)
The high quality microbial proteins
become available to the ruminant
when the microbes are digested
The microbes supply the host
animal with vitamin B complex,
provided there is an adequate
supply of the trace element cobalt
for B12.
Tree goats - Morocco
4
GWR 227206 Integrative Veterinary
Physiology
Disadvantages of a Ruminant
Ruminants must spend
~ 4-7 hours per day gathering food
~ 8 hours per day chewing the cud
Failure to effectively expel the
large volumes of gas produced
during fermentation can be life
threatening
Ruminants have no direct control
over the digestive activities of the
microbes
Can indirectly influence the rate of
fermentation
5
GWR 227206 Integrative Veterinary
Physiology
Disadvantages of a Ruminant
End products of fermentation are
mainly the volatile fatty acids
(VFAs)
acetic, propionic and butyric acids,
Pathways for intermediary
metabolism must be geared to
their use.
Propionic acid is the only VFA
capable of being converted to
glucose
The ruminant has a high glucose
requirement during the later
stages of foetal growth and
lactation.
Propionic acid
Acetic acid
Butyric acid
6
GWR 227206 Integrative Veterinary
Physiology
Disadvantages of a Ruminant
In the wild state these
disadvantages may be of little
consequence.
Under intensive farming systems
easily fermented concentrates
often replace the normal roughage
diet
Physiological strategies regulating
fermentation may be unable to
cope with the greatly increased
rate of VFA production
Can cause a variety of digestive
and metabolic disorders.
7
GWR 227206 Integrative Veterinary
Physiology
Ruminant Stomach
Ruminants have a single „compound‟ stomach divide into 4 distinct
divisions.
Fermentation occurs in the first three, reticulum, rumen and
omasum, which are non-secretory
Collectively referred to as the forestomach.
The 4th division, abomasum, is the „true‟ stomach and is analogous
to the simpler form of stomach found in dogs, cats and humans
It secretes hydrochloric acid, which kills the microbes and sterilises
the digesta.
Pepsinogen produced by the abomasum begins the breakdown of
protein, mainly microbial cell wall protein.
8
GWR 227206 Integrative Veterinary
Physiology
Ruminant Stomach – Right Side
ventral sac abomasum
omasum
reticulum
9
GWR 227206 Integrative Veterinary
Physiology
Ruminant Stomach – left Side
reticulumabomasum
Ventral rumen
Caudal
Blind sac
atrium dorsal sac
10
GWR 227206 Integrative Veterinary
Physiology
Forestomach
The interior surface
of the rumen forms
numerous papillae
that vary in shape
and size from short
and pointed to long
and foliate.
Reticular epithelium is
thrown into folds that
form polygonal cells that
give it a honey-combed
appearance. Numerous
small papillae stud the
interior floors of these
cells
The inside of the omasum
has broad longitudinal
folds, reminiscent of the
pages in a book. The
omasal folds represent ~
1/3rd of the total surface
area of the forestomach
11
Innervation of Ruminant Stomach
The innervation to the stomach
Vagus nerves
splanchnic nerves,
Both supply motor (efferent), and
sensory (afferent) nerves.
The left and right vagi merge in the
lower thoracic region and then divide
to form dorsal and ventral branches
Vagal (parasympathetic) efferent
activity is essential for the orderly and
sequential contractions of the
forestomach
Stimulation of splanchnic motor
(sympathetic) nerves inhibit motility
GWR 227206 Integrative Veterinary
Physiology 12
Innervation of Ruminant Stomach
GWR 227206 Integrative Veterinary
Physiology
to celiacmesenteric ganglion
to liver & pylorus
Dorsal vagus
Ventral vagus
Reticulum
Rumen
Abomasum
Omasum
From: Dyce, K. M., et al (1996) Textbook of Veterinary Anatomy. 2nd Edition. W.B Saunders Company
13
Innervation of Ruminant Stomach
There is a predominance of sensory over motor fibres in the vagal (10:1)
and splanchnic (3:1) nerves, hence both are predominantly sensory nerves
The vagal sensory fibres innervating the stomach are associated with:
Tension receptors
slowly adapting mechanoreceptors
located in the muscle layers
activated by
passive distension of the stomach
active contraction of the smooth muscle of the stomach wall
Epithelial/mucosal receptors.
rapidly adapting mechanoreceptors and chemoreceptors
are most numerous in the reticulum, cranial sac of the rumen, abomasum (and
duodenum)
respond to tactile stimuli (light brushing), acids, alkali and hyper- and hypotonic solutions
The splanchnic sensory fibres transmit information from serosal receptors, which
are especially concentrated at the attachment of the mesenteries.
GWR 227206 Integrative Veterinary
Physiology 14
Blood Supply to Ruminant Stomach
The blood supply to the stomach is via branches of the
celiac artery.
Blood flow to the stomach increases markedly after
feeding when fermentation end products are being
absorbed.
The nutrient rich blood drains into the portal vein and
passes through the liver before being returned to the
heart via the caudal vena cava.
GWR 227206 Integrative Veterinary
Physiology 15
Blood Supply to Ruminant Stomach
GWR 227206 Integrative Veterinary
Physiology
From: Dyce, K. M., et al (1996)
Textbook of Veterinary Anatomy.
2nd Edition. W.B Saunders Company
16
Microbial Fermentation
The microbes in the forestomach are mostly
anaerobic bacteria, but also yeast-like fungi and
protozoa.
They break down the ingesta by hydrolysis and
anaerobic oxidation.
The protozoa feed on ruminal bacteria, starch and
polyunsaturated fatty acids in the ingesta.
They are very sensitive to changes in intraruminal
conditions and their presence in ruminal fluid is a
good indicator of its „normality‟.
Very little is known about the importance of the
ruminal fungi in fermentation.
GWR 227206 Integrative Veterinary
Physiology
Rumen protozoa
Rumen fungi
Rumen bacteria
17
Microbial Fermentation
The plant structural carbohydrates in
roughage are β-1,4 linked glucose units
(cellulose) and β-1,4 linked xylose units
(hemicellulose)
Slowly broken down by the ruminal cellulolytic
bacteria to VFAs.
Carbohydrate in grain-based feed contains α-
linked glucose units
rapidly degraded by amylolytic bacteria to VFAs and
lactic acid.
Both types of bacteria are classified as
primary bacteria
Secondary bacteria convert the lactic acid to
propionate and hydrogen to methane.
This last reaction re-oxidises reduced co-
enzymes making them available again as
hydrogen acceptors.
A small amount of O2 is taken in with the food
and water; some O2 diffuses from arterial
blood across rumen wall
Quickly used up by facultative anaerobic bacteria
GWR 227206 Integrative Veterinary
Physiology
Cellulose
Starch
18
Ruminant Digestion
The digesta in the forestomach do not form an
homogenous mass
Instead the most recently ingested food is added
to a raft of fibrous material that floats on the
underlying soupy fluid
Above this raft is a layer of ruminal gas
During clinical examination, palpation of the
lumbar fossa should detect the gas layer above
the textured fibrous raft.
Failure to remove (by eructation) the gas causes
distension of the stomach (bloat)
Excessive hardness of the raft is a sign of
ruminal impaction, and softness or absence of
the raft indicates the animal has not recently
consumed roughage
GWR 227206 Integrative Veterinary
Physiology
From: Dyce, K. M., et al (1996)
Textbook of Veterinary Anatomy.
2nd Edition. W.B Saunders Company
19
Digestion in the Rumen
GWR 227206 Integrative Veterinary
Physiology
Animal Organ Acetic Propionic Butyric
Sheep Rumen 64 20 16
Ox Rumen 71 15 14
Horse Caecum 73 20 7
Dog Colon 51 36 13
Average composition of the mixed volatile fatty acids from the rumen and large
intestine, given as percentages of total acid. (Adapted from AT. Phillipson, Nutr. Abstr.
Rev., 17:12-18, 1947-48.)
20
Digestion in the Rumen
Most of the VFAs produced by the microbes are absorbed into the venous
blood across the wall of the forestomach and used by the ruminant as
substrates for metabolism.
About half of the VFAs are absorbed in an undissociated state by passive
diffusion
the remainder is absorbed by facultative diffusion in exchange for
bicarbonate
During absorption, most of the butyrate is metabolised to β-hydroxybutyrate
used as a substrate by most tissues, and especially the mammary gland during
lactation.
About 1/3 of the propionate is metabolised to lactic acid during absorption.
Most of the acetate is absorbed unchanged.
GWR 227206 Integrative Veterinary
Physiology 21
Protein Digestion/Regeneration
GWR 227206 Integrative Veterinary
Physiology
About half the dietary protein is degraded in the forestomach
Overfeeding of protein can lead to excessive levels of ammonia production, ammonia
toxicity and energy expenditure for conversion (detoxification) of ammonia to urea in the
liver
Dietary Nitrogen
Salivary urea
Amino acid
synthesis
Tissue
proteins
22
Rumen Gases
The production of gases by
the microbes reaches a
peak of up to 40 L/h in
cattle 2-4 hours after a
meal, when fermentation
rate is at its maximum.
The principal gases
produced are CO2 (60%),
CH4 (30-40%) and variable
amounts of N2, H2S, H2 and
02.
They are eliminated almost
entirely by the process of
eructation.
GWR 227206 Integrative Veterinary
Physiology
Composition of rumen gases in a dairy cow. From L.E. Washburn
and S. Brody, Mo. Ag. Exp. Sta. Res. Bull.: 263, 1937.
24
Control of Fermentation
Ruminants exert limited control over the rate at which
fermentation proceeds by altering or satisfying several
requirements. These include: The regular supply of macerated substrate (chewed food) for microbial digestion.
Removal of the end products of fermentation (VFAs, microbial products, gases).
The movement of undigested particles to the abomasum, and thence to the small
intestine.
Mixing of the forestomach contents to prevent local accumulations of inhibitory
end products, and aid absorption of VFAs.
Providing a highly buffered fluid environment for the micro-organisms.
Providing stable conditions of temperature, osmotic pressure, and pH.
GWR 227206 Integrative Veterinary
Physiology 25
Salivary Secretion
Ruminants produce large volumes
of saliva Sheep: 6-16 L/day
cf blood volume ~ 3.5 litres
Cattle: 60-160 L/day cf blood volume ~ 40 litres
The secretions from the major
glands are isotonic with blood plasma
have no significant amylase activity
change their composition following salt
depletion (K+ exchanged for Na+ due to
the action of aldosterone),
contain urea and alkali
maintain a basal secretory rate even
after denervation.
The main salivary glands of the sheep (from Kay, 1960).
1: parotid, 2: submaxillary (submandibular), 3: inferior molar,
4: sublingual, 5: buccal, 6: labial. Glands are paired on both
sides of the head and mouth.
GWR 227206 Integrative Veterinary
Physiology 26
Salivary Secretion
The reticulum, rumen and omasum produce no secretion of their own and depend for the
provision of a liquid medium on: water contained in food
water in drink
saliva
The parotid glands are serous glands provide the major fraction of salivary secretion into the rumen.
In sheep a single gland may secrete 1-4 L/day,
In cattle, estimates for a single gland range from 20-80 L/day
Parotid saliva is approximately isotonic with tissue fluid helps stabilise the osmotic environment for the microbes.
Has a high electrolyte content:
The high levels of HCO3 and HPO4-- are important for their buffering action and maintaining a pH
range of 5.5 - 7.0 despite VFA production.
Urea in parotid saliva provides an energy source for the microbes
GWR 227206 Integrative Veterinary
Physiology
Na+ K+ HCO3- HPO4
-- Cl-
Saliva
(mmol/l) 170 13 112 48 11
Plasma
(mmol/l): 140-180 3.9-5.4 ~27 2-7 95-105
Electrolyte concentrations in ruminant parotid saliva
27
Control of Salivary Secretion Salivary glands are
innervated by
parasympathetic and
sympathetic divisions of
ANS
GWR 227206 Integrative Veterinary
Physiology
Courtesy Dr J Patterson, Swinburne University, Melbourne
28
Control of Salivary Secretion
As in other animals afferent stimuli arise in the mouth from taste and
mechanical stimulation of the gums.
In ruminants, important sensory inputs also arise from lower in the gut.
Moderate stretch in several areas of the gut is an effective excitatory
stimulus to parotid secretion. Oesophagus - especially the thoracic part
The opening of the oesophagus (the cardia)
The reticulum- especially on its medial wall near the reticular groove and reticulo-omasal
orifice
Omasal canal
Vagal afferent fibres carry excitatory stimuli from these regions to salivary
centres.
Ensures a steady flow of saliva enters the rumen even when the animal is
not eating or ruminating
The stimuli mentioned so far all increase or excite parotid secretion
GWR 227206 Integrative Veterinary
Physiology 29
Control of Salivary Secretion
The stimuli mentioned so far
all stimulate parotid secretion
Recordings in conscious
animals suggest there are also
inhibitory mechanisms
operating
When sheep and cattle eat
Initially there is a very high rate
of secretion from the parotid
glands
After about 30 minutes of
eating this declines and falls to
below pre feeding levels
This is despite the fact that
feeding continues and
excitatory stimuli from taste,
buccal and oesophageal
stimulation are present
GWR 227206 Integrative Veterinary
Physiology
Parotid and submandibular salivary secretion rates during eating.
Submandibular flow is shown by the dotted line and parotid flow by the
solid line. Feeding is marked by F and rumination by R. (From D.H.
Carr, pers comm)
30
Control of Salivary Secretion
Possible inhibitory stimuli:
High (excessive) levels of stretch of the
oesophageal and gastric regions mentioned
earlier will inhibit salivary secretion
Mediated by vagal and splanchnic afferent
nerves
Important as digesta and secretions
accumulate in the stomach
Increases in blood osmotic pressure reduces
parotid secretion.
Plasma osmolality may increase by over 5%
during feeding Increased metabolite production in gut
Movement of water into gut
Drop in blood volume
Reduction in salivary flow helps maintaining
stable conditions in the ECF during
digestion.
GWR 227206 Integrative Veterinary
Physiology
Changes in the osmolality of jugular plasma, the rate of parotid salivary
secretion and reticular contractions before and during feeding. (From D.H.
Carr, pers comm).
31
Control of Salivary Secretion
Sympathetic actions on the gland Decrease the blood supply through vasoconstriction
Cause contraction of myoepithelial cells within the gland and expulsion
of saliva
Followed by compensatory pause in flow as myoepithelial cells relax
Add protein to the saliva
GWR 227206 Integrative Veterinary
Physiology 32
Salivary Secretion
In summary, the principal functions of saliva in ruminants are to:
Return urea to the rumen for microbial protein synthesis.
Add fluid for proper microbial actions in the large reticulorumen fermentation vat.
Supply bicarbonate and phosphate buffers to keep the pH of the reticulorumen
within the normal limits (5.5 to 7.0)
GWR 227206 Integrative Veterinary
Physiology 33
Motility of Reticulum & Rumen
Several different methods can been used to study motility of the
reticulum and rumen in intact animals
Palpation
Auscultation
Intragastric pressure changes recorded using balloons or open tipped
catheters positioned in the stomach via
Nasogastric tube
Rumen fistula
Radiography
Barium sulphate (insoluble)
Radio-opaque markers surgically attached to stomach wall
Electromyography
Partial Exteriorisations
GWR 227206 Integrative Veterinary
Physiology 34
Partial Exteriorisations
Partial exteriorisations are prepared by bringing small parts of the reticulum
and rumen into a position immediately beneath the skin. Contractions of the
stomach are then seen as skin movements.
GWR 227206 Integrative Veterinary
Physiology
Method of partially exteriorising the rumen. The circles represent
stitches. (From C.S.W. Reid, Proc. N.Z. Soc. Anim. Prod., 23: 169-
188.)
35
Reticulorumen – A sequence
Two basic types of contraction sequence
The first commences with a double contraction of the
reticulum
Contraction then spreads from the cranial to the
caudal regions of the rumen
Involves dorsal rumen first and then ventral rumen
This is a “backward” moving contraction.
GWR 227206 Integrative Veterinary
Physiology 36
Reticulorumen – A sequence
This type of contraction has been variously termed: Primary contraction.
Mixing cycle
A sequence
It recurs in sheep at about 30-90 sec - at the shorter
interval if the animal has been recently fed, and toward
the longer if fasted.
The functions of the contraction include: Mixing of digesta and distribution of microbes
Mechanical breakdown of digesta
Bringing the products of fermentation to absorptive surfaces
Aiding the movement of digesta onward in the gut
GWR 227206 Integrative Veterinary
Physiology 37
Reticulorumen – B sequence
The second type of contraction does not involve the
reticulum
Starts as a contraction of caudal ventral blind sac
Spreads to posterior then anterior regions of dorsal
rumen
Ends with a contraction of ventral rumen sac
This is a “forward” moving contraction.
GWR 227206 Integrative Veterinary
Physiology 38
Reticulorumen – B sequence
This contraction has been variously termed:
Secondary contraction.
Eructation (belching) cycle.
B sequence.
B sequences follow a variable time after A sequences - not always
in a 1:1 ratio.
Animal will eructate (belch) with this contraction, depending on the
rate of gas production.
GWR 227206 Integrative Veterinary
Physiology 39
Control of RR Motility
Organised movements of the reticulum and rumen cease after
the vagus nerves have been cut
after atropine has been administered
The evidence from anaesthetised animals indicates that both sensory and
motor fibres controlling RR contractions are contained in the vagus nerves
In anaesthetised animals reticulum contractions can be caused by
Stimulation of the intact vagus nerve.
Stimulation of the peripheral end of the cut cervical vagus nerve.
Stimulation of the central end of a cut cervical vagus nerve, provided the other
vagus nerve is intact.
The vagi contain both motor (efferent) fibres to the stomach and sensory
(afferent) fibres from it, both of which are normally involved in the regulation
of gastric contractions
GWR 227206 Integrative Veterinary
Physiology 40
Control of RR Motility
Mechanical stimulation (touch or stretch) of the regions of the gut
listed below is an effective stimulus to contractions of the reticulum
and rumen.
The mouth (gums)
Thoracic oesophagus
Reticulum (especially medial wall)
Reticulorumenal fold
Reticulo-omasal orifice
Slight stretch of the abomasum
All these are areas that would normally be stimulated during eating
and digestion
GWR 227206 Integrative Veterinary
Physiology 41
Vagus Indigestion
„Vagus indigestion‟ (abnormal motility patterns of RR) is due to damage to
receptor areas rather than to vagi themselves - especially damage around
medial wall of reticulum
GWR 227206 Integrative Veterinary
Physiology
A nail is embedded in the
epithelium of the reticulumA nail has penetrated the
reticulum, causing traumatic
reticuloperitonitis (hardware
disease) and the death of this cow
Images from Noah’s Arkive, University of Georgia.
Metal door spring removed from
a cow‟s reticulum
42
Control of RR Motility
Chemical stimuli delivered to the gut may also be involved in reflex
stimulation of RR contractions.
The addition of HCl at pH 1to the abomasum stimulates reticular
contractions, provided the vagal branches to the abomasum
remained intact.
This observation has been criticised because abomasal pH rarely
falls below pH 2.5.
However acid is secreted by parietal cells at about pH 0.9
Provided the receptors are close to the site of acid secretion,
stimulation would be possible.
GWR 227206 Integrative Veterinary
Physiology 43
Control of RR Motility
Co-ordination of the afferent
information from chemo- and
mechano-receptors occurs in reflex
centres.
These are located in the dorsal vagal
nucleus of the medulla oblongata
They regulate the efferent vagal
discharge.
Inhibitory as well as excitatory stimuli
influence the activity of the medullary
centres.
Excess stretch is inhibitory.
Generally this applies to any of the
areas where moderate stretch is
excitatory, but especially to the
abomasum.
GWR 227206 Integrative Veterinary
Physiology 44
Detecting Contractions of Reticulum
and Rumen in “the field”
Reticular contractions
identified by a tinkling sound
heard through stethoscope
Caused by rumen fluid flowing
back into reticulum as it relaxes
Contraction of rumen detected
by palpation in sub lumbar
fossa region
A hardening and bulging caused by
contraction of dorsal rumen
This allows A sequences and
B sequences to be
distinguished seperately
GWR 227206 Integrative Veterinary
Physiology 45
New-Born Ruminant Stomach
The forestomach in the new-born ruminant is anatomically and functionally under-developed
It contains no microbes (i.e. is sterile) and does not contribute significantly to the digestion milk
GWR 227206 Integrative Veterinary
Physiology
Rumen
Reticulum
Omasum
Abomasun
Age in weeks
Weig
ht as a
perc
enta
ge o
f birth
weig
ht
(birth
weig
ht
= 1
00)
Abomasum
Omasum
Oesophagus
Dorsal sac
Rumen
Ventral
sac
Pylorus
Posterior
Blind sacs
Small intestine,
caecum & colon
46
Rumen Development
GWR 227206 Integrative Veterinary
Physiology
Rumen
Oesophagus
Omasum
Reticulum
Birth to 2 weeks
Abomasum
Oesophagus
ReticulumOmasum
Abomasum
Rumen
Oesophagus
Abomasum
Rumen
Omasum
Reticulum
Oesophagus
Rumen
Abomasum
OmasumReticulum
8 weeks
3-4 months Mature
Rob Costello, Dairy Technical Specialist, Merrick's Inc.
47
New-Born Ruminant Stomach
In the new-born ruminant, swallowed milk is directed from the oesophagus directly into
the omasum and abomasum by the reticular groove.
When contracted forms a conduit between the cardia and the reticulo-omasal orifice
GWR 227206 Integrative Veterinary
Physiology
From: D.A. Titchen and J.C. Newhook,
1975. In Digestion and Metabolism in the
Ruminant. pp 15-29. Editors IW. McDonald
and A.C.I. Warner. Australia, University of
New England Publishing Unit.
48
New-Born Ruminant Stomach
Within the abomasum, the newly ingested colostrum and milk is subjected
to the clotting action of the enzyme rennin.
Rennin has a pH optimum of near 6.5 and produces a hard clot or curd
consisting of the butterfat and the curd proteins (caseinogens) precipitated
as calcium caseinate)
The whey fraction, which contains important immunoglobulins, passes into
the small intestine
The antibodies are absorbed, passively immunising the young animal
In cattle the immunoglobulins constitutes about 70% of the whey protein of
colostrum
The immunoglobulins survive digestion in the gut because: Neonates are achlorhydric, i.e acid, and pepsin, secretion is absent or low
Colostrum contains an inhibitor to the proteolytic enzyme trypsin.
GWR 227206 Integrative Veterinary
Physiology 49
New-Born Ruminant Stomach
The immunoglobulins are absorbed by pinocytosis
They coalesce to form a single large globule in the basal portion in the cell
There are both specific, receptor mediated absorption mechanisms, and non-specific absorption
mechanisms
egg albumin, gelatin and serum protein added to the colostrum is also absorbed
Adrenocortical hormones appear to cause premature „closure‟ of the gut
Such hormones are produced under conditions of stress
Lambs born under stressful conditions (climatic or nutritional) may have impaired globulin
absorption.
GWR 227206 Integrative Veterinary
Physiology
Species Prenatal Postnatal
Ox, Goat, Sheep 0 +++ (36 hr)
Pig 0 +++ (36 hr)
Horse 0 +++ (36 hr)
Dog + ++ (l0 days)
Rat + ++ (20 days)
Rabbit +++ 0
Man +++ 0
Transmission of Passive immunity and time after birth for „gut closure‟.
50
Reticular Groove
Milk taken when young ruminants suck passes directly to the abomasum
The milk flows directly to the abomasum where the enzyme rennin causes coagulation
This delays its passage into the intestine
Other swallowed fluids, e.g. saliva, are directed into the reticulum
The reticular groove forms a channel from the oesophagus, through the reticulum to the reticulo-
omasal orifice.
It has two well defined „lips‟ which flank a floor.
The lips make a functional extension of the oesophagus directly to the reticulo-omasal orifice.
GWR 227206 Integrative Veterinary
Physiology 51
Reticular Groove – Reflex Control
Contraction of the reticular
groove occurs as a reflex
response.
When the vagi are cut,
suckled milk enters the
reticulorumen.
In decerebrate
preparations the
reticular groove can be
made to contract by introduction of water into
the posterior region of the
mouth cavity
touching the posterior
mouth cavity with a probe
Cranial laryngeal nerve
stimulation (sensory)
GWR 227206 Integrative Veterinary
Physiology 52
Reticular Groove – Reflex Control
The responses of the reticular groove illustrate many of the classical
properties of visceral reflexes.
Latency: 2 -4 seconds may elapse between delivery of stimulus and contraction of the groove. .
Summation: One afferent stimulus alone is often insufficient to excite a visceral reflex.
Introduction of water alone into the mouth, or stimulation of afferent fibres in the cranial laryngeal nerve, is
ineffective.
Inhibition: Groove closure inhibited when the abomasum is full/stretched (vago-vagal reflex).
Causes spillage of milk into the reticulum and rumen.
The rapid ingestion of a large volume of milk (e.g. once a day feeding) may
cause ineffective clotting of the curd and rapid emptying of the abomasum.
This in turn results in overloading of the small intestine with protein,
bacterial overgrowth in the intestine and diarrhoea (scours).
GWR 227206 Integrative Veterinary
Physiology 53
Reticular Groove – Adult Animals
In about 70% of adult sheep the reticular
groove can be made to contract by giving
copper salts orally
This has been used to direct drenches
against nematodes directly to the
abomasum
Nicotine and arsenic were the active
components of the drenches
To achieve a lethal concentration for the
worms (not the sheep) they had to be
delivered to the site of parasite action
(abomasum)
In adult cattle sodium salts have the effect of
causing groove contraction
From time to time there is a resurgence of
interest in using the reticular groove
mechanism to aid animal production
GWR 227206 Integrative Veterinary
Physiology 54
Reticulo-Omasal Orifice (ROO)
Passage of material from the reticulum
to the omasum occurs via a relaxed
ROO, which in sheep is about 1 cm in
diameter.
In the cow, for the greater part of the A
sequence, the ROO is loosely open
(some 60-70% of the time).
During the first phase of the diphasic
reticular contraction the orifice closes,
it opens at the peak of the second
phase of contraction of the reticulum
Relaxation (opening) of the ROO is
controlled by the vagus
The neurotransmitter is most likely VIP
GWR 227206 Integrative Veterinary
Physiology
Reticulum
R.O.O.
Pressure recordings
(balloon)
Motility of the Reticulo-Omasal Orifice
R.O.O.
55
Reticulo-omasal Orifice (ROO)
When the ROO opens, digesta
flow into the omasum and the
omasum relaxes
Relaxation of the omasum
combined with contraction of the
reticulum contributes to the flow
of digesta into the omasum
Contractions of the omasum can
be inhibited by distension of the
abomasum
This may provide a means for the
abomasum to control the volume
of ingesta entering it
GWR 227206 Integrative Veterinary
Physiology
Pressure records
Reticulum
R.O.O.
Omasum
56
Omasum
The function of the omasum is unclear.
May help regulate flow of digesta from the
reticulorumen to the abomasum
Fluid and electrolyte and VFAs are absorbed by the
omasum.
The surface area of the leaves is large - about 1/3 of
the total epithelial lining of the reticulorumen
The leaves undergo movement, especially near their
bases.
Contractions stimulated by infusions of VFAs into the
omasal lumen.
May not be essential for life
Some ruminants, e.g. primitive deer, (lesser mouse
deer) have no omasum. This is a browsing type of
ruminant
GWR 227206 Integrative Veterinary
Physiology
Omasal folds
57
Eructation
Removal of gas produced by micro-organisms during fermentative digestion
Gas produced in the first 3 divisions of the ruminant stomach
Rate of production increases after eating and decreases slowly until the
next feeding.
Most of the gas is produced in the reticulorumen
Estimated that 1.2 - 2 litres of gas are formed per minute in the rumen of a
500 kg cow.
Most of the gas is the result of bacterial action and CO2 liberation from
salivary bicarbonate
GWR 227206 Integrative Veterinary
Physiology
CO2 CH4 N2 O2 H2 H2S NH3
65% 27% 7% 0.60% 0.20% Trace Trace
58
Dorsal Rumen
Oesophagus
Reticulum
Ventral Rumen
Caudal Ventral
Blind Sac
Eructation
Eructation usually begins with a B
sequence contraction.
This sweeps gas toward the
oesophagus at the cardia.
Whether eructation occurs at this
stage depends on clearing the cardia
of ingesta
The sphincter at the diaphragm
relaxes, and the oesophagus fills with
gas
When the oesophagus has filled with gas the diaphragmatic sphincter closes and the
pharyngo-oesophageal sphincter relaxes
Gas moves up the oesophagus - in cattle aided by a rapid anti-peristaltic wave of
contraction in the oesophagus - perhaps passively in sheep
GWR 227206 Integrative Veterinary
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GWR 227206 Integrative Veterinary
Physiology
From: Van Soest, Peter J (1994) Nutritional Ecology of the Ruminant, Edition: 2nd. Publisher: Comstock Publishing
60
Ruminant Methane Production
GWR 227206 Integrative Veterinary
Physiology
Since 1999 atmospheric methane
concentrations have levelled off
World population of ruminants has
increased at an accelerated rate
Prior to 1999 there was a strong
relationship between change in
atmospheric methane
concentrations and the world
ruminant populations
Since 1999 this strong relation has
disappeared.
This change in relationship
suggests that the role of ruminants
in greenhouse gases may be less
significant than originally thought
Global large ruminant equivalence and atmospheric methane
concentrations
Large ruminant equivalence (*1,000,000)
Methane concentration (ppb)
Figure 1. Global atmospheric methane concentrations from NOAA (2007) and
cattle equivalents from FAO (2007). Large ruminant equivalences are calculated
using 8 sheep or goats as being equivalent to a large animal
1850
1800
1750
1700
1650
1600
1550
1500
FAO: Food and Agriculture Organisation
IAEA: International Atomic Energy Agency
NOAA: National Oceanic and Atmospheric Administration
1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2005
Year
61
Ruminant Methane Production
Large ruminants produce some 15-
20% of the global production of
methane
Ruminants on low quality feeds
possibly produce over 75% of the
methane from the world's population of
ruminants
Supplementation can reduce methane
production as
% digestible energy consumed
per kg live-weight gain
GWR 227206 Integrative Veterinary
Physiology
R. A. Leng Department of Biochemistry, Microbiology and Nutrition,
University of New England, Armidale, N.S.W. 2351
No supplements
Urea/mineral
supplements
No supplements
Urea/mineral
+ bypass protein
supplements
The effects of supplements on methane emissions for
ruminants on low feeds. (A) The effects of improving the
efficiency of rumen fermentative activity on methane production/kg
of digestible energy consumed. (B) the production of methane/kg
gain in supplemented cattle (feed conversion efficiency (FCR)
(9:1) or un supplemented cattle (FCR = 40:1) fed straw-based diets
(after Saadullah 1984)
% d
ige
stib
le e
ne
rgy
Fe
rme
nte
d to
me
tha
ne
(A) (B)
Me
tha
ne
pro
du
ctio
n
(kg
/to
n L
wt. G
ain
)
20
15
10
5
0
1200
800
400
0
62
FCR is the mass of the food eaten divided by the body mass gain over a
specified time
Control of Eructation
GWR 227206 Integrative Veterinary
Physiology
Gaseous distension of the rumen stimulates eructation and secondary contractions of the rumen
Occurs only if the animal is in an upright or nearly upright position
Does not occur under general anaesthesia
Caused by stimulation of receptors in the caudal region of the dorsal sac of the rumen,
Is a vago-vagal reflex.
Receptors in the cranial part of the rumen and reticulum are important in determining whether or
not eructation occurs with the secondary contractions
Eructation does not occur when the area around the cardia is covered with ingesta, water, foam
This is important because any liquid that was regurgitated into the mouth with the eructated gas
can enter the airways and lungs (glottis open during eructation).
Fluid
No cardiac
opening
Cardiac
Opening Distension Distension Secondary cycles
63
Eructation
Other stimuli, apart from gaseous
distension of the rumen, are
important in causing eructation
Feedlot cattle in USA are often
subject to a chronic and appetite-
depressing bloat when fed a
concentrate food.
This can be corrected by ensuring
the incorporation of some
scabrous material (roughage) in
the diet.
Apparently tactile stimulation of
the RR is important
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Rumination
Rumination is the process by which
ingesta are regurgitated, rechewed, re-
ensalivated and reswallowed.
This second period of mastication
appears to have two main functions: To reduce food particles size.
To facilitate microbial attack on the plant
material
Comparisons have been made of the
rate of digestion of lucerne stalks
placed in nylon bags in the rumens of
sheep.
The lucerne was cut either
transversely or longitudinally, placed in
a nylon bag and then examined at
intervals with scanning EM.
GWR 227206 Integrative Veterinary
Physiology
Cut transversely
Unaltered after
40 hrs
Cut longitudinally
Unrecognisable
After 6-7 hrs
65
Rumination
Rumination has been shown to be very effective in reducing particle
size of food
Observations were made on sheep with oesophageal fistulae
Boluses were collected on their way to or on their way from the
mouth (after re-chewing)
GWR 227206 Integrative Veterinary
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Particle size To mouth From mouth
Coarse 30% 10%
Medium 37% 51%
Fine 33% 39%
66
Rumination
Involves both the digestive and respiratory systems.
Rumination is characterised by:
An extra reticular contraction before the normal diphasic contraction
Respiration momentarily stops and an inspiratory effort made against a glottis at
the peak of the extra phase of reticular contraction
The bolus moves rapidly up the oesophagus to the mouth.
Excess fluid from the bolus is swallowed
Bolus is remasticated
The process is completed in 45-60 seconds by re-swallowing the
bolus.
The whole sequence is repeated after the previous bolus is re-
swallowing.
Rumination commonly continues for an hour or more.
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Electromyogram (EMG)
Recordings During
Rumination in a Sheep
A. EMG of reticulum showing
normal biphasic contraction
B. A normal biphasic contraction
preceded by an extra
contraction
C. EMGs of the oesophagus near
the glottis (1), upper thorax (2)
and close to the cardia (3), and
the reticulum (Re)
D. Jaw and respiratory
movements
The regurgitation phase (AP) of
rumination is closely followed
by swallowing of the excess
liquid on two occasions (P1
and P2) and later of the bolus
(P3).
GWR 227206 Integrative Veterinary
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A.
B.
C.
D.
68
Rumination
Periods of rumination
and feeding in sheep and
cattle on legume pasture
Although diurnal patterns
differ, both species tend
to graze in the morning
and evening and rest
during the hotter part of
the day
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Rumination
The physical nature of the diet influences the age at which rumination commences
It may begin in lambs and calves as soon as two weeks after birth
A diet containing roughage causes rumination to start earlier than a diet of solely
milk.
The drive for roughage is strong - milk fed calves will eat the wooden rails of pens and lambs
pull wool from other lambs and chew and swallow it
Tactile stimulation (touch) or light stretch particularly of the area around the cardia,
reticular groove, reticulo-ruminal fold and reticulo-omasal orifice is very effective.
Thus the desire to ruminate seems to be related in large part to the volume of
contents in the reticulorumen, and to the tactile stimulation by coarse material in the
rumen
Rumination is associated with characteristic changes in the demeanour of animals
and often occurs at night.
A reduction in external stimuli (visual and auditory) may be a pre-requisite.
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Rumination
Current theories on the basis of rumination suggest that
the initial reticular contraction at the time of regurgitation
has two functions: To flood the area of the cardia with ingesta which is then available for
regurgitation.
To raise the pressure in the stomach - there may be an increase of 5-6
mm Hg during this contraction.
The inspiratory effort against a closed glottis produces a large reduction
in pressure within the thorax, and hence within the thoracic oesophagus.
The steep gastric-oesophageal pressure gradient - it may be 40-60 mm
Hg in cattle – drives the movement of digesta into the oesophagus when
it relaxes.
The bolus is then swept to the mouth by a reverse peristaltic wave.
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Abomasum
The abomasum is structurally and histologically comparable to the simple stomach of monogastric
animals.
There are three regions which are defined by the type of gland:
A very small cardiac region encircling the omasoabomasal orifice which has cardiac glands
The body or fundus which contains gastric or fundic glands
The pyloric region which contains pyloric or antral glands.
The body has large spiral mucosal folds and this results in about 90% of the total surface area
being formed by the body region. The pyloric region consists of the antrum, which has no folds but
only surface rugae, the pyloric canal and sphincter.
GWR 227206 Integrative Veterinary
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Pyloric sphincterOmasoabomasal orifice
73
Abomasum – Gastric Glands
In the fundic region, the glands
contain parietal (or oxyntic) cells which
produce HCl
chief (or peptic) cells which produce
pepsinogen
mucous neck cells
The chief cells are present in the
lower third of the gland
The parietal cells occupy much
of the middle third
Endocrine cells are found mainly
in the lower part of the gland
The gastric pits are lined with
surface epithelial cells.
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Abomasum
The cardiac glands contain the same cell types as the
fundic glands.
There are is larger number of mucous cells which
produce a very viscous mucus.
The pyloric (antral) glands are coiled and produce both
mucus and pepsinogen,
There are virtually no parietal cells.
The gastrin-secreting G cells are present in antral
glands.
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Abomasum
The composition of gastric juice in the ruminant is similar to that in
other mammals
pH averages about pH 2.8
contains pepsin and intrinsic factor
The principal functions of the abomasum are:
Digestion of protein through action of pepsin
Rumen microorganisms entering the abomasum are killed by the acid and
digested to provide nutrients for the host
Secretes intrinsic factor which is essential for absorption of Vitamin B12 in the
ileum
In the immature ruminant the abomasum secretes the enzyme rennin which
causes rapid clotting of milk.
Pepsin is also produced in the preruminant animal and is involved in proteolytic
digestion of the milk
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Abomasal Secretions
Both abomasal secretion and the inflow
of digesta from the omasum are
continuous.
Sheep secrete about 5 litres of gastric
juice per day.
The volume, acidity and pepsin content
increase with feeding and rumination,
decreases with starvation
Experimental sheep may also develop a
conditioned secretory response to the
sight and smell of food.
Abomasum secretions
stimulated by vagal nerve stimulation,
cholinomimetics
Inhibited by atropine i.e. parasympathetic
blockers
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Abomasal Secretions
Control of abomasal secretions
can be studied using surgically
prepared pouches
GWR 227206 Integrative Veterinary
Physiology
Secretion from pouch increases
when animal feeds
78
Abomasal Secretions
The increase in abomasal secretion with feeding is associated with an
increased inflow of digesta into the abomasum.
Part of the response due to distension of the stomach which is one of the
known stimuli to abomasal secretion in ruminants
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Abomasal Secretions
Distension also stimulates the release of the antral hormone gastrin.
Gastrin secretion is important in ruminants (as well as monogastrics) in mediating food-stimulated gastric secretion.
The composition of the digesta coming into the abomasaum appears to be a key factor.
Gastrin is released by ammonia and peptone in the abomasal fluid and when the pH of the abomasal contents rises.
The high pH of incoming digesta appears to be a powerful stimulant to gastrin release in the sheep
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Abomasal Parasites
Abomasal nematodes
Ostertagia circumcincta (sheep) 0stertagia ostertagi (cattle)
Trichostrongylus axei
Heamonchus contortus
All impair the secretory activity of the abomasum.
The abomasal pH rises since acid secretion is inhibited, serum
gastrin increases and there may also be raised serum pepsinogen
levels.
Diarrhoea, reduced digestibility and disturbed protein metabolism
and utilization
The high serum gastrin may reduce both rumino reticular and
abomasal motility and also the animal‟s appetite.
H. contortus is a blood-sucker and can cause serious anaemia and
death.
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