Protein degradation in the rumen of sheep and cattle.

Abstract

AbstractSheep and steers were given, at a maintenance level of feeding, four diets consisting of either poor quality dried grass, good quality dried grass or separate mixtures (63:35) of each of the dried grasses and barley. Ammonia and total N concentrations in rumen liquor were significantly higher in sheep than in steers whereas total volatile fatty acid concentration was significantly lower and protein N concentration, pH and rumen fluid dilution rate did not differ significantly between species. For all rumen measurements, except total volatile fatty acid concentration, there were significant differences between diets with the dietary responses being similar in both species. Protein degrading activity in the rumen was measured in vitro with casein as the substrate and in situ by measuring N disappearance when soyabean meal, cotton seed meal, groundnut meal, meat and bone meal, fish meal and dried grass were incubated in polyester bags in the rumen. Casein degrading activity of rumen liquor did not differ significantly between species, whereas rumen in‐situ degradation of all feedstuffs, except fish meal, was significantly higher in sheep. In both species, ruminal casein degrading activity was higher when the good quality forage was given than when the poor quality forage was given and also increased when part of each forage was replaced by barley. In contrast, rumen in‐situ degradability of feedstuffs did not differ when the two all‐forage diets were given and the inclusion of barley in the diet reduced the rate of degradation. In both species and with all diets the rumen in‐situ degradability ranking of the feedstuffs was similar.