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Digestive physiology and feeding behaviour of equids – a comparative approach
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FEB 09, 2023
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Take home messages
- Like other members of their order – the perissodactyla or odd-toed ungulates – equids had a much richer species diversity in fossil times than they have today.
- The main reason for their decline is seen in the comparative success of artiodactyls – even-toed ungulates – and amongst these, especially of ruminants.
- Possible reasons for the comparative success of ruminants in evolutionary time include locomotion (where a single hoof precludes use of swampy or rocky habitats), higher water dependency due to lack of a ‘selective brain cooling mechanism’, a slower overall reproductive rate due to slower in utero maturation, and digestive physiology.
- The digestive physiology of equids, compared to ruminants, is summarized as lower digestive efficiency compensated by higher intake levels (which also necessitates more time spent foraging).
- Historically, this has been linked to differences in fermentation site (foregut vs hindgut fermentation) and digesta retention times.
- Historically, it has been postulated that equids are at an advantage during times of low forage quality, because they are supposed to be able to increase intake in such a situation. The graphical depiction of this theory has been widely reproduced, in spite of a lack of support for it by empirical data.
- Empirical data so far suggests no fundamental difference in the reaction of equids and ruminants to decreasing forage quality (increasing fibre levels): a reduction of ad libitum intake. • Preliminary data suggests that horses may be more susceptible to food scarcity (constrained food intake) than ruminants.
- In contrast to ruminants, the digestive tract of horses does not selectively discriminate by particle size.
- A major difference between equids (and other nonruminants) and ruminants is chewing efficiency.
- Among nonruminants, equids achieve extremely high chewing efficiency, most likely due to their cheek tooth surface anatomy (elaborate enamel folds).
- Ruminants achieve an even higher chewing efficiency, not because of dental anatomy, but due to the sorting mechanism in their forestomach.
- Because particle size-reducing chewing is postponed to rumination in ruminants, their ingestive behaviour and ingestive chewing pattern differs from that of equids. Equids chew more thoroughly during ingestion, with a chewing pattern similar to that used by ruminants during rumination.
- It is an interesting question how extant equid species survived in their respective habitats together with ruminant presence.
References
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- Arnold GW (1984) Comparison of the time budgets and circadian patterns of maintenance activities in sheep, cattle and horses grouped together. Applied Animal Behaviour Science 13: 19-30
- Clauss M, Dittmann MT, Müller DWH, Zerbe P, Codron D (2014a) Low scaling of a life history variable: analysing eutherian gestation periods with and without phylogenyinformed statistics. Mammalian Biology 79: 9-16
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- Janis CM, Constable EC, Houpt KA, Streich WJ, Clauss M (2010) Comparative ingestive mastication in domestic horses and cattle: a pilot investigation. Journal of Animal Physiology and Animal Nutrition 94: e402-e409
- Janis CM, Bernor R (2019) The evolution of equid monodactyly: a review including a new hypothesis. Frontiers in Ecology and Evolution 7: 119
- Langer P (1987) Der Verdauungstrakt bei pflanzenfressenden Säugetieren. Biologie in unserer zeit 17: 9-14
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- Shoemaker L, Clauset A (2014) Body mass evolution and diversification within horses (family Equidae). Ecology Letters 17: 211-220
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How to reference this publication (Harvard system)?
Clauss, M. (2023) “Digestive physiology and feeding behaviour of equids – a comparative approach”, EEHNC - Virtual Congress - 2021. Available at: https://www.ivis.org/library/eehnc/eehnc-virtual-congress-2021/digestive-physiology-and-feeding-behaviour-of-equids-–-a-comparative-approach (Accessed: 07 June 2023).
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