Peptides are intermediates in the conversion of ingested protein to ammonia in the rumen and their accumulation depends upon the nature of dietary protein (Mesgaran & Parker, 1995). In addition, It has been demonstrated that the hydrolysis rate of peptides was influenced by peptide structure and that proline containing peptides were hydrolysed more slowly by rumen fluid (Mesgaran & Parker, 1996). The objective of the present experiment was to investigate the effect of altering the sources of protein, in diets with similar effective rumen degradable protein (ERDP), on the ruminal peptide-N concentrations.

Four Iranian Baloochi lambs weighing 33±1.3 Kg, each with a permanent rumen fistula, were fed twice daily with diets differing in protein sources in a 42 latin square design. The diets consisted of a basal diet of chopped lucerne, barely and sugar beet pulp (190, 230 and 170 g DM d–1, respectively) which was supplemented with lucerne (L), cottonseed meal (C), soybean meal (S) or molasses+urea (M+U) (210, 118, 84 and 80+9 g DM d–1, respectively).