Abstract
Four mature pony geldings weighing an average of 134 kg and fitted with ileal cannulas were used in two 4X4 Latin square experiments to determine the digestibility of forage and soybean meal protein in different segments of the equine digestive tract. Chromic oxide was fed in both trials to measure ileal flow and fecal excretion. Digestion and absorption of nitrogen was determined from changes in nitrogen:chromium ratios, and true digestion of nitrogen was computed by regression analyses. In trial 1, four diets containing varying ratios of chopped bermudagrass and alfalfa hays were fed. True total tract nitrogen digestibility was 89.6%. True digestibility of forage nitrogen in the small intestine was 40.5% in this trial, while true postileal digestibility was 78.1%. These data indicate that almost 90% of forage protein was digested over the total digestive tract. Approximately 45% of the digestible forage nitrogen was digested prececally with the remaining nitrogen being digested postileally. Thus, when ponies were fed all forage diets the lower tract was a major site for protein digestion. In trial 2, a basal, corn-based diet and three diets with soybean meal as the primary source of protein were formulated to contain approximately 5%, 9.5%, 14% and 16.5% crude protein as fed. True total tract digestion of nitrogen was 95.3%. True digestibility of feed (SBM) nitrogen in the small intestine over the range of linearity was 72.2%, while true digestibility of nitrogen reaching the large intestine was 89.8%. These data indicate that the protein in soybean meal was almost completely digested in the equine digestive tract. Further, while results from this trial indicate there may be an upper limit to the quantity of SBM nitrogen digested in the small intestine from a meal, approximately 75% of the digestible SBM protein was digested prececally when nitrogen intake was less than approximately 125 mg/kg body weight/feeding.
Farley, Eleanor Baker (1995). Digestion of protein in the equine small and large intestines. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -F375.