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Year: 2010
Comparative ingestive mastication in domestic horses and cattle:a pilot investigation
Janis, C M; Constable, E C; Houpt, K A; Streich, W J; Clauss, M
Janis, C M; Constable, E C; Houpt, K A; Streich, W J; Clauss, M (2010). Comparative ingestive mastication indomestic horses and cattle: a pilot investigation. Journal of Animal Physiology and Animal Nutrition,94(6):e402-e409.Postprint available at:http://www.zora.uzh.ch
Posted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.ch
Originally published at:Journal of Animal Physiology and Animal Nutrition 2010, 94(6):e402-e409.
Janis, C M; Constable, E C; Houpt, K A; Streich, W J; Clauss, M (2010). Comparative ingestive mastication indomestic horses and cattle: a pilot investigation. Journal of Animal Physiology and Animal Nutrition,94(6):e402-e409.Postprint available at:http://www.zora.uzh.ch
Posted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.ch
Originally published at:Journal of Animal Physiology and Animal Nutrition 2010, 94(6):e402-e409.
1
COMPARATIVE INGESTIVE MASTICATION IN DOMESTIC HORSES AND
CATTLE: A PILOT INVESTIGATION
Christine M. Janis1, Emily C. Constable1,2, Katherine A. Houpt3, W. Jürgen Streich4,
Marcus Clauss5*
1Department of Ecology and Evolutionary Biology, Brown University, Providence, RI
02912, USA
2Currently Emily Pershing: 5 Crystal Lane, Cumberland, ME 04021, USA
3Department of Clinical Science, College of Veterinary Medicine, Cornell University,
Ithaca, NY 14853, USA
4Leibniz Institute of Zoo and Wildlife Research (IZW) Berlin, 10315 Berling, Germany
5Clinic of Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of
Zurich, CH-8057 Zurich, Switzerland, mclauss@vetclinics.uzh.ch
*to whom correspondence should be addressed
Running head: Chewing in horses and cattle
2
Summary
It is often assumed that horses chew food more intensively during ingestion than cattle,
which – as ruminants – complete part of the mastication during rumination. This has been
proposed as a reason for more robust mandibles, larger masseter insertion areas and
larger masseter muscles in horses as compared to cattle and other grazing ruminants.
Here, we evaluate results of comparative feeding trials with three horses (338-629 kg)
and three cows (404-786 kg), on four different roughages. Ingestion time (s/g dry matter)
and chewing intensity (chews/g dry matter) differed among animals within a species,
indicating an influence of body mass, and differed significantly between different
forages. However, although numerical differences clearly suggest that horses have longer
ingestion times and higher chewing intensities on high-fiber roughage than do cattle, this
could not be proven in this dataset, most likely due to the small number of individuals
sampled. Further studies are required to corroborate the suspected ingestive behavior
difference between equids and ruminants.
Keywords: Craniodental anatomy, Chewing intensity, Equids, Ingestion, Mastication,
Ruminants
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Introduction
Equids (horses, donkeys and zebra) and large grazing bovids (such as cattle, other
bovines such as bison, and alcelaphine antelope such as wildebeest) are similar in many
aspects of their biology. In terms of their ecology they occupy similar habitats (e.g., both
zebra and wildebeest are grazers, common on the African savannas), and both have
adaptations for a high degree of ingesta particle size reduction (Fritz et al. 2009).
However, they differ fundamentally in several aspects of their digestive physiology (Janis
1976) and may select different plant species and plant parts (e.g. Hansen et al. 1985).
Horses are hindgut fermenters that achieve ingesta particle size reduction by a
sophisticated dental design, and have adopted a strategy of a high food intake, fast ingesta
passage, and a comparatively low digestive efficiency. In contrast, bovids are foregut
fermenters with a specific sorting mechanism in their forestomach that facilitates not only
extreme particle size reduction, but also a longer ingesta passage with a higher digestive
efficiency. Bovids show a lower overall food intake than equids (of similar body size),
but have an increased food intake as compared to nonruminant foregut fermenters (Foose
1982; Duncan et al. 1990; Jernvall et al. 1996; Stevens and Hume 1998; Clauss et al.
2007; Clauss et al. 2009a; Schwarm et al. 2009). Direct comparisons in foraging patterns
between horses and cattle are rare; however, Arnold (1984) and Duncan et al. (1990)
observed longer daily grazing times in horses as compared to cattle or sheep, and Menard
et al. (2002) observed a higher food intake in free-ranging horses as compared to cattle in
the same habitat.
The concept of a higher food throughput in horses has been implicated in different
studies on the craniodental design of herbivores. A higher food intake should, in theory,
translate into more robust anatomical structures associated with ingestion. Additionally, it
4
has been suggested that the fact that ruminants perform a part of their chewing activity on
‘cud’, i.e., material soaked in rumen fluid and softened by the effect of bacterial digestion,
would mean that there would be an overall reduced load on their masticatory system (as
opposed to these animals doing this same amount of chewing on undigested forage)
(Fortelius 1985). Equids are known to have larger masseter muscles than ruminants, and
also a larger mandibular masseter insertion area (Turnbull 1970), and finite element
analysis shows that hindgut fermenters have more robust jaws than ruminants of similar
size and diet (Fletcher et al. 2009). While grazing ruminants generally tend to have a
shorter premolar tooth row than browsers, no reduction of the premolar tooth row is
observed in perissodactyls (beyond the reduction or loss of the first premolar seen in all
ungulates), and there is even the opposite trend for a more pronounced premolar row
(especially in terms of the molarization of the premolars) in grazing as compared to
browsing perissodactyls (Janis 1990; Mendoza et al. 2002). Consequently, the total
occlusal surface area (and the total occlusal volume) in horses is larger than that of
ruminants of similar diet (Janis 1988). Corresponding to these different findings, higher
bite forces were measured in horses than in cattle (Hongo and Akimoto 2003).
The behavioral correlate of these observations would be an increased ingestive
chewing intensity, and a longer ingestion time per unit of food, in equids as compared to
ruminants. Ruminants initially swallow large particles (Clauss et al. 2009b) and reduce
their size later via rumination, while horses chew their food only once and nevertheless
achieve comparatively small ingesta particles (Fritz et al. 2009). Data on ingestion time
have frequently been recorded for cattle and horses (Table 1). However, these data do not
allow concise conclusions as to differences in the chewing behavior of cattle and horses
because of the large range overlap in the data, and the fact that no single study compares
5
horses and cattle under the same conditions. Compilations of literature data are hampered
by the fact that chewing behavior is influenced by the fiber content of the diet (cattle:
Armentano and Pereira 1997; horses: Meyer et al. 1975; Gallagher and Hintz 1988; Scott
and Potter 1989; Ellis et al. 2005); the physical state of the food (cattle: Shaver et al. 1988;
Woodford and Murphy 1988; Mcleod et al. 1990; other ruminants: Mcsweeney and
Kennedy 1992; Gross et al. 1995); the body size of the animal (cattle: Bae et al. 1983;
horses: Meyer et al. 1975; mammals in general: Druzinsky 1993; Shipley et al. 1994;
Gerstner and Gerstein 2008); variation in intraspecific dental morphology (red deer:
Pérez-Barberìa and Gordon 1998); and the overall intake level (cattle: Bae et al. 1981;
Shaver et al. 1988). Direct comparisons of ingestion and mastication behavior between
equids and ruminants, under identical conditions and with common test diets, are, so far,
unfortunately lacking.
In order to compare the ingestion time, the chewing frequency and the chewing
intensity between horses and cattle, we re-evaluated data generated during a trial that
determined the number of chews during the ingestion of defined amounts of various test
diets in individual horses and cattle of different body weights (previously presented as
conference abstracts, Janis and Constable 1993; Constable et al. 1994). We predicted that
the horses would display a greater number of chews per unit ingested food, and hence a
longer ingestion time per unit food compared to the cattle, and that this difference would
increase with increasing levels of fiber in the food. We also predicted that the horses
generally would have a lower chewing frequency than cattle, as in the data collection of
Gerstner and Gerstein (2008), due to the mechanical constraints of their heavier
mandibles, and that within any one group (horses or cattle) smaller animals would display
a higher rate of chewing than larger ones, due to simple allometric scaling, where chewing
6
frequency and number of chews per unit ingested food are assumed to scale negatively to
body mass (Druzinsky 1993; Shipley et al. 1994; Gerstner and Gerstein 2008).
Methods
This experiment was conducted at the Cornell University College of Veterinary
Medicine, Department of Physiology, in the summer of 1992, and was approved by
Cornell University’s Institutional and Animal Care Use committee.
Animals and Diets
Six animals were used in this study, three horses and three cows (Table 1). Animals
were maintained on a diet of mixed hay (including alfalfa hay, timothy hay, straw, and
clover) fed twice daily together with a supplement of corn, oats, and molasses. Water was
available at all times. Prior to testing, animals were fasted for eight to ten hours by
removing all leftovers from the previous meal and withholding the morning meal, in
order to ensure prompt intake of the test meals in all animals and remove effects of
satiety.
Three experimental diets of hay of differing fiber content were used in the
experiment – alfalfa hay, timothy hay, and a mixed hay similar to the one used for
maintenance of the animals. Alfalfa hay was lowest in total cell wall (neutral detergent
fiber, NDF) and lignocellulose (acid detergent fiber, ADF) content; timothy hay
resembled the mixed hay in total cell wall and alfalfa hay in lignocellulose contents; and
the mixed hay had the highest lignocellulose content (Table 2). Additionally, freshly cut
pasture grass was used that resembled the timothy hay in its fiber content, but had a much
lower dry matter (DM) content than the dried forages (Table 2).
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Experimental Procedure
Animals were fitted with halters that detected chewing movements as changes in
pressure in a small foam-filled balloon placed underneath the mandible. Pressure changes
were recorded via a pressure transducer on a Grass model 7-D polygraph. In general,
each chewing-induced pressure change was recorded as a deflection on a graph paper
record. Any deflections caused by movements other than chewing were noted by an
observer as they occurred, and were discounted in the analyses.
Each animal received four tests meals of each forage during a period of one day.
Alfalfa hay, the mixed hay, and freshly cut grass were tested on two consecutive days
each, resulting in a total of eight tests per animal and diet; timothy hay was only tested
during one day with a total of four tests per animal. Tests were performed between eleven
am and one pm in all animals.
Exactly a hundred grams of each test diet was offered to the animals in a feed bin
raised 70 cm above ground level. During each test, food spilled by the animals was picked
up by the observer and placed back into the bin. The barn in which the tests were
performed was locked during the procedure to ensure no disturbance for the animals. Each
test run was terminated either when all food was ingested, or when all significant chewing
was complete and animals began to play with left-over stems. The amount of leftovers was
consistently negligible.
Analyses
Results were expressed as the ingestion time for the whole diet or its cell wall
component (s/g DM or s/g NDF, respectively), as the chewing frequency (chews/s), and
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the chewing intensity (chews/g DM or chews/g NDF, respectively). Results are reported
as means ± standard deviation per species and diet.
ANOVA with species and diet as fixed factors and animal (nested in species) as
random factor, with subsequent post hoc tests (Dunnet T3 test because of inequality of
variances) was used to test for potential differences. Linear contrasts (after sorting the
animals with respect to their body weight) served to test for a correlation between the
body mass and the chewing variables. For further explorative analysis, we additionally
performed an ANOVA with species and diet as fixed factors and body mass as a covariate
using pooled data, ignoring the animals as factor (i.e., pretending all individual
measurement derived from different individual animals). In an explorative analysis, small
p-values have no confirmative power. The significance level was set to α=0.05. The SPSS
16.0 (SPSS Inc., Chicago, IL, USA) statistical software package was used for the
statistical calculations.
Results
When observation time was plotted against the total number of chews, differences
between the species were only evident in those trials in which ingestion time was
prolonged, with a higher chewing frequency in cattle (Fig. 1). Numerical differences in
ingestion times and chewing intensity between the species were as expected (Table 4 &
5). Except for feeding on fresh grass, horses also had a numerically lower chewing
frequency than cattle.
The explorative analysis resulted in highly significant influence of species, diet, and
body mass on ingestion times, with significant diet*species interaction, indicating that the
pattern between the species changed with diets (Fig. 2). That is, for the more fibrous diets
9
the horses spent a longer time chewing than did cattle of similar body mass. For chewing
intensity, highly significant influence of species, diet, and body mass on ingestion times
were also indicated, with significant diet*species interaction (see Fig. 3); species only
tended towards significance (p=0.072) when chewing intensity was based on neutral
detergent fiber, but the diet*species interaction term remained highly significant. Here
again, with the most fibrous diet, the chewing intensity (number of chews per unit of dry
matter) was greater in the horses than in the cows. For chewing frequency, the same
pattern was found, with horses displaying lower frequencies than cattle (see Fig. 1), but
here body mass only tended towards significance (p=0.078), most likely due to the
unusually low chewing frequency in the smallest horse (data not shown).
In the final statistical analyses, differences in parameters between individual
animals within species were always significant (Tables 4 & 5), suggesting an effect of
body mass. In both horse and cattle, linear contrasts indicated correlations of all
parameters with body mass (p always <0.001). In contrast to the explorative analyses,
differences between the species were not statistically significant once the fact that
multiple measurements were performed on the limited number of individuals was taken
into account (Tables 4 & 5). Differences between the diets were often significant (Tables
4 & 5), with fresh grass requiring more time to ingest and more chews per unit of food.
Between the three dried forages, differences between alfalfa hay and the other two hays
were significant when the amount of dry matter was the reference unit, but were not
significant when the amount of cell wall ingested was the reference unit.
Discussion
10
Although the dataset evaluated here shows certain predicted trends, such as an
increased ingestion time and chewing frequency with increasing dietary fiber content, or
an association between ingestion time and chewing intensity and body mass (as suggested
for equines by Mueller et al. 1998), the sample size was too small to allow definite
conclusions about species differences between horses and cattle. However, the numbers
do lend credence to the notion that, especially on more fibrous diets, horses chew their
food more thoroughly on first ingestion than do cattle, as would be expected for a hindgut
fermenter eating more food per day than a ruminant of similar size and diet, and having
only the opportunity at initial ingestion to reduce the particle size of the food. Our results
suggesting that cattle have a higher rate of chewing than horses is also supported by
Putnam’s (1986) study of horses and cattle in the New Forest (England). Here the horses
(New Forest ponies) were observed to take fewer bites per minute than cattle in each
season, and this difference was more pronounced on lower quality grasslands.
However, while the findings supported the expectations numerically, differences
between the species could not be corroborated statistically. In order to decide whether the
numerical trends are really spurious, whether such differences actually do occur,
experiments with a larger number of individuals are required. The data of this study,
which must be considered preliminary, suggests that differences between the species
might be most evident on high-fiber roughages. The fact that differences between the
three forages of similar dry matter content – the three hays – were significant when
expressed on a dry matter basis but not when expressed on a fiber basis (Tables 4 & 5)
indicates that chewing investment is directly linked to the fiber content of the diet. When
comparing the data from this study to that of others, it should be noted that due to the
long fasting regime in the experimental animals used here, chewing rates might be
11
considered “maximum chewing rates”, because animals were probably hungrier than they
would ever be under natural circumstances.
When considering the total chewing activity of horses and ruminants, it is important
to note that ingestive chewing is less important in ruminants and often contributes less to
overall chewing efficiency than rumination (Trudell-Moore and White 1983). Overall,
horses have shorter chewing times per unit ingested food if not only ingestive but also
ruminative mastication is included in the comparison (Mueller et al. 1998), but as
previously noted, the food masticated during rumination is of a different nature (in terms
of likely abrasive quality and toughness) than the food on initial ingestion. Whether the
difference in craniodental morphology between equids and ruminants can truly be related
to differences in feeding behavior depends not only on comparative measurements of
ingestive mastication, but even more on physical characteristics of regurgitated rumen
contents as compared to ingested food. The assumption that regurgitated ingesta is
‘softer’, requires less forceful chewing, and that ruminants can therefore afford less
robust mandibles and smaller masseter insertion areas than equids, should be tested by
applying mechanical tests to different ingesta and digesta fractions, ideally gained from
esophagus-fistulated animals. Well-founded speculations, such as shorter ingestion times
in ruminants, and higher ingestive chewing intensity in horses as compared to cattle on
high-fiber diets, remain to be conclusively corroborated.
Additional studies might also reveal whether the interspecific trend of decreasing
chewing frequencies with increasing body mass (e.g. Druzinsky 1993; Shipley et al.
1994) can also be observed within species; in this pilot investigation, there was no
influence of body mass on this parameter in cattle, and even an inverse relationship in
horses. In contrast, the reported negative interspecific allometry of chewing intensity with
12
body mass (Shipley et al. 1994) was evident in this dataset within species as well (Fig. 3).
The reason for this difference is probably that the negative allometry of chewing
frequency with body mass is rather low at BM-0.13 to BM-0.18 (Druzinsky 1993; Shipley et
al. 1994), whereas that of chewing intensity is much more pronounced at BM-0.85 (Shipley
et al. 1994); thus, chewing frequency may be much more prone to misrepresentation in
low sample size datasets. However, when plotting the results on chewing frequency from
this study and other measurements made in horses fed hays from the literature (Fig. 4), it
appears that available data for horses is rather in line with the general mammalian trend
as reported by Shipley et al. (1994). As for differences between horses and cattle, it is to
be expected that the heavier mandibles of horses, with their more robust bone structure
and higher tooth mass, move at a lower frequency than the more slender mandibles of
cattle.
The craniodental apparatus of equids (and other hindgut fermenters) is more
robustly built than that of ruminants, and we propose that this morphological difference is
functional in origin, rather than merely a phylogenetic artifact. The data presented here
are at least supportive of the hypothesis that horses chew their food more intensively on
initial ingestion than do cattle: this, and the fact that many hindgut fermenters ingest
more food per day than ruminants of equivalent diet and body size, supports the
functional hypothesis that the greater degree of craniodental robustness of hindgut
fermenters reflects a greater amount of stress on the masticatory apparatus.
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Table 1. Ingestion times (seconds per gram dry matter) in domestic cattle, horses and donkeys
Diet Cattle Horse Donkey Straw 2.5 - 3.5 2.9 - 8.0 Grass hay 1.2 - 2.4 1.8 - 4.8 7.2 Haylage 1.7 - 1.8 Grass silage 1.9 - 3.5 Concentrates 0.2 - 0.6 0.5 - 0.9 (data from Balch 1971; Meyer et al. 1975; Mueller et al. 1998; Ellis and Hill 2005; Müller 2009)
Table 2. Animals used in the trials
Species ID Body mass (kg)
Age (a)
Sex
Horse H1 338 7 gelding Horse H2 605 19 female Horse H3 629 12 female Cow C1 404 20 female Cow C2 659 5 female Cow C3 786 6 female
Table 3. Roughages used in the trials and their content of dry matter (DM, in % wet weight),
neutral detergent fiber (NDF, in % DM) and acid detergent fiber (ADF, in % DM)
Food DM NDF ADF Alfalfa hay 92.4 44.5 34.2 Timothy hay 95.1 59.4 34.7 Mixed hay 92.2 61.3 41.4 Fresh grass 24.4 57.8 35.3
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Table 4. Ingestion time (per unit dry matter or neutral detergent fiber) in horses (n=3) and cattle
(n=3)
---------------- Ingestion time ---------------- (s/g dry matter) (s/g NDF) Diet Horses Cattle Horses Cattle Alfalfa 1.57 ± 0.43 1.50 ± 0.53 3.52 ± 0.98 3.37 ± 1.18 Timothy 2.46 ± 0.44 1.69 ± 0.63 4.14 ± 0.75 2.85 ± 1.05 Mixed 2.82 ± 0.69 1.68 ± 0.57 4.60 ± 1.13 2.74 ± 0.93 Fresh grass 3.92 ± 1.23 3.27 ± 0.90 6.78 ± 2.13 5.65 ± 1.55 ANOVA p p Species 0.325 0.354 Diet <0.001 grass>mix/tim>alf <0.001 grass>mix/tim/alf Animal(species) <0.001 <0.001
Table 5. Chewing frequency and intensity (per unit dry matter or neutral detergent fiber) in horses
(n=3) and cattle (n=3)
Diet ------ Chewing frequency ------ ------------------------- Chewing intensity ------------------------- (chews/s) (chews/g dry matter) (chews/g NDF) Horses Cattle Horses Cattle Horses Cattle Alfalfa 1.23 ± 0.14 1.30 ± 0.12 1.88 ± 0.40 1.96 ± 0.72 4.24 ± 0.90 4.41 ± 1.62 Timothy 1.04 ± 0.09 1.25 ± 0.13 2.54 ± 0.40 2.14 ± 0.93 4.27 ± 0.67 3.60 ± 1.56 Mixed 1.13 ± 0.12 1.18 ± 0.13 3.16 ± 0.74 2.01 ± 0.82 5.16 ± 1.21 3.27 ± 1.33 Fresh grass 1.20 ± 0.11 1.12 ± 0.16 4.61 ± 1.17 3.62 ± 1.08 7.97 ± 2.03 6.26 ± 1.87 ANOVA p p p Species 0.589 0.396 0.430 Diet <0.001 mix/tim/grass<alf <0.001 grass>mix≥tim/alf <0.001 grass>mix/tim/alf Animal(species) <0.001 <0.001 <0.001
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Figure 1. Chewing frequency (number of chews vs. unit time) in all individual experiments with horses and cattle from this study.
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a
b
c
Figure 2. Ingestion time (seconds per gram dry matter) in horses and cattle of different body mass fed (with increasing fiber content) a) alfalfa hay, b) timothy hay, c) a mixed hay (repeated measurements in three individuals of each species).
a
b
c
Figure 3. Chewing intensity (chews per gram dry matter) in horses and cattle of different body mass fed (with increasing fiber content) a) alfalfa hay, b) timothy hay, c) a mixed hay (repeated measurements in three individuals of each species).