Proteolytic activity of ruminal digesta during the feeding cycle in sheep receiving grass hay/concentrate or maize silage/concentrate diets.

Proteolytic activity was measured by the digestion of 14C-labelled casein in digesta removed from the rumen of four sheep receiving a grass hay/concentrate diet and four sheep receiving a maize silage/concentrate diet. Samples were removed immediately before feeding and at 2-h intervals after feeding up to 12 h. Animals on both diets produced similar proteolytic activities (1.83 (S.D. 0.41) and 2.14 (S.D. 0.61) mg 14C-casein hydrolysed (ml ruminal fluid)-1 h-1 with the maize silage- and grass hay-based diets, respectively). Time after feeding had no effect on proteolytic activity, but between-animal variation was consistent and highly significant, with the highest-activity animals having activities 64 and 74% higher than the lowest-activity animals on the two diets, respectively.