Excessive protein breakdown and ammonia production often lead to inefficient N utilisation in ruminants. Peptides are intermediates in the breakdown process. The aims of this study were to characterize peptidase activities of rumen bacteria and to determine which species of bacteria were responsible for the different steps of peptide breakdown in the rumen.

Four rumen-fistulated adult sheep received a mixed diet (hay, barley, molasses, fishmeal and minerals and vitamins: 500, 99.5, 100, 91 and 9.5 g/kg dry matter respectively) fed in equal meals of 500 g at 0800 and 1600 h. Rumen fluid was removed 3 h after the morning feeding, strained, and mixed bacteria were prepared by differential centrifugation. Bacteria were sonicated and debris was removed by centrifugation. Peptidase activities were determined on the supernatant fluid.