Utilization of proteins by the equine species.

Protein digestion, nitrogen retention, plasma protein, plasma urea, and plasma-free amino acids were determined for ponies fed 3 different protein supplements. Substitution of casein, corn gluten meal, or corn gluten meal plus lysine for a portion of the cornstarch in a low-protein basal ration increased apparent digestion of protein. Substitution with either casein or corn gluten meal plus lysine produced a significant increase (P less than 0.05) in nitrogen retention, whereas the corn gluten meal substitution did not. Nitrogen retention, expressed as percentage of nitrogen absorbed, was increased significantly (P less than 0.05) by the addition of casein to the basal ration. Significant change in plasma protein concentration did not occur when different sources of protein were added to the basal ration, but plasma urea nitrogen increased significantly (P less than 0.05) in the ponies given the casein variation of the ration. Lysine supplementation resulted in a marked increase in plasma lysine concentration. Seemingly the equine species responds to differences in the quality of dietary protein.