Variation of proteolytic activity in ewe during in vivo digestion of two pea-based diets differing by their fermentability characteristics.

In order to study the effects of a small difference in starch and nitrogen availability on proteolysis, two different diets were supplied to four ewes fitted with rumen fistulae. They differed in the ratio of fermentable nitrogen over fermentable energy. with 144 g of fermentable nitrogen (FN) per kg of fermentable energy (FE) for diet I and 126 g FN x kg(-1) FE for diet II. The diets were constituted of 700 g hay grass, 200 g ground pea and either 100 g ground wheat (diet I) or 100 g corn starch (diet II). After two weeks of an adapting period to the diets, rumen content was sampled after feeding over time. The rate of disappearance of soluble proteins was 2.5 times higher with diet II and ammonia concentrations were significantly lower (from -28 to -43%) with diet II. Total proteolytic activity, by considering all the bacterial compartments, was significantly higher with diet II (+40 EU/mL x h(-1)): changes in the total proteolytic activity in the particulate and the liquid phases of the rumen could explain the difference observed between the two diets. Moreover, with diet II, exopeptidase activities increased more in the liquid phase, especially leucine aminopeptidase and Dipeptidyl peptidase I (DPP-I), and the diversity of endopeptidase activities increased in the particulate phase. These two facts could account for the higher total proteolytic activity in the rumen content with diet II.