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APPENDICES Appendix A The Digestive Physiology of the Horse and Its Interrelationship with Feeding Ecology of the Equidae A report for the National Research Council Committee on Wild and Free-Roaming Horses and Burros by Montague W. Demment Department of Zoology University of Wisconsin, Madison Introduction The overall purpose of this review is to provide an interpretive perspective of the digestive and nutritional characteristics of the horse. This perspective is aimed primarily at understanding the way digestion and nutrition in this species affect its overall ecology, encompassing both its interactions with its food supply via diet and other herbivores, primarily cattle. Although this paper reviews the literature, it does so selectively. The emphasis has been to include key papers that enable digestion to be related to equid ecology. Extensive and recent reviews of horse nutrition and digestion are already available in the literature (Olsson and Ruudvere 1955, Mehren and Phillips 1972, Frape and Boxall 1974, Robinson and Slade 1974, Frape 1975, Hintz 1975, Hintz and Schryver 1973). The horse is a herbivorous animal which extracts substantial energy from the structural carbohydrates of plant material. To accomplish the digestion of these carbohydrates, vertebrates must rely on a symbiotic relationship with bacteria and protozoans (Moir 1968). This digestion occurs by a process of fermenration in the gut. Although the products of fermentation are widespread in the G.I. tract (Elsden et al. 1946), they are usually concentrated in a site within a particular section of the tract. This fermenta- tion site provides not only a protected environment of the proper pH for the microbes, but also the ability to slow down the passage of fibrous particles for more complete fermentation. 259