Cyclic changes in ionic composition of digesta in the equine intestinal tract

Effects of diet and time after feeding on osmolality and inorganic ion content of gastrointestinal digesta were studied in 24 ponies. Animals, fed either a conventional or a low-protein, high-cellulose diet, were sacrificed 2, 4, 8, or 12 h after a meal. Animals fed the conventional diet showed cyclic variations in the ionic composition and osmolality of digesta with time after feeding. The most marked variations were seen in the contents of the stomach and small colon. However, results also indicated a cyclic appearance and disappearance of Na in large intestinal contents that correlated with net appearance and disappearance of volatile fatty acid (VFA) and H2O. Since Na and VFA were the major solutes absorbed from the cecum and colon, the ionic composition and water content of large intestinal digesta appeared largely dependent on the rate of microbial digestion. Although the large intestine of animals fed the experimental diet contained approximately twice the quanity of Na, K, Cl, VFA, and H2O, COMPENSATORY ABSORPTION BY THE MOre distal segments of colon resulted in little additional loss of these in the feces.