Physiology of intake and digestion in Equine animals

Abstract

This review focuses on some recent advances in our understanding of the physiological mechanisms involved in intake and digestion. Different factors, either intrinsic or external to the individual, which can impact the intake and digestion of feeds are discussed with a special focus on the effect of feeding practices and exercise of sport and race horses so far removed from their natural environment. Exercise probably has an impact on the physiology of intake and digestion but it is not well documented mainly due to methodological limits. The motivation of a horse for ingesting a feedstuff is strongly influenced by the feed palatability (related to the smell, taste, appearance or texture). Feed intake integrates probably the nutritive value of a feed as well as its hedonic value or its aversion value. There is also large individual variation that should be taken into account when feeding different horses. It seems that gastric or cecal repletion had no effect on subsequent feeding behaviour. Feed intake is regulated on a short term by glucose and acetate and by leptin and ghrelin hormones and on a long term by the nutritional needs of the organism, which are modified by on the physiological status, activity and thermoregulation. Regarding the implication on energetic yield, digestion in horses shall be studied in the various compartments of the digestive tract. Most studies are conducted on apparent digestibility and mean retention time in the total gastro-intestinal tract which limits the comprehension of partial digestibility. Digestion of starch starts in the stomach with enzymes from the host and originated from abundant autochthonous microorganisms. In the small intestine, digestion is primarily under the control of the host enzymatic secretions that breakdown carbohydrates, fat and protein. Microbial cell-walls degradation occurs in the favourable ecosystem of the hindgut.