THE SIGNIFICANCE OF SMALL VS LARGE INTESTINAL DIGESTION OF CEREAL GRAIN AND OILSEED PROTEIN IN THE EQUINE

Mature ponies fitted with permanent ileal cannulas were used in two 3x 3 Latin square experiments to quantify prececal, postileal and total t ract digestion of N. In trial 1, corn, oats and sorghum were each fed with coastal Bermuda grass hay in 75:25 ratios. Apparent prececal dige stibilities were similar (P>.05) and averaged 46.6%. By-difference pro cedures were employed to calculate digestibility of the cereal grain N only and apparent prececal N digestibility averaged 57.1%. In trial 2 , a basal corn and hay diet was supplemented with cottonseed meal and soybean meal. Apparent total tract N digestibilities were similar (P>. 05) across treatments, and prececal digestibility averaged 45.6%. By-d ifference calculations were used to determine digestibility of SBM and CSM N alone. Apparent prececal digestibility of SBM was 52.5% and was lower (P<.05) than 81.2% for CSM. It is possible that inadequate or e xcessive heat treatment of SBM affected enzymatic digestion. True dige stibility of total rations fed in trial 2 was estimated by linear regr ession of nitrogen digested on nitrogen intake or N presented to the l arge intestine, True N digestibility of diets containing SBM and CSM w as 54.7% and 69.4%, respectively.