DIGESTION OF SOYBEAN-MEAL PROTEIN IN THE EQUINE SMALL AND LARGE-INTESTINE AT VARIOUS LEVELS OF INTAKE

Four mature pony geldings weighing an average of 134 kg and fitted wit h ileal cannulas were used in a 4 x 4 Latin square experiment to deter mine the digestibility of soybean meal (SBM) protein in different segm ents of the equine digestive tract at various levels of protein intake . A complete basal corn-based diet was supplemented with SBM to formul ate four diets with increasing crude protein. The diets, labeled A (ba sal), B, C and D, contained 4.9%, 9.5%, 14% and 16.5% crude protein (a s fed), and provided nitrogen, per feeding, at approximately 44.8, 84. 3, 123.9 and 146.3 mg/kg of body weight, respectively. Chromic oxide w as fed to measure ileal flow and fecal excretion. Digestion and absorp tion of nitrogen was determined from changes in nitrogen:chromium rati os, and true digestion of nitrogen was computed by regression analysis . True total tract digestion of nitrogen was 95.7%. True digestibility of 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 SBM was almost com pletely digested in the equine digestive tract, Furthermore, approxima tely 75% of the digestible protein was digested prececally when nitrog en intake was less than approximately 125 mg/kg of body weight per fee ding.