Nitrogen metabolism in the sheep. Protein digestion in the rumen

Abstract

Measurable amounts of a-amino nitrogen (0.3-1.5 mg/100 ml), and of a-amino nitrogen which is liberated on hydrolysis of the diffusible peptides (0.2-1.0 mg/100 ml), are present in rumen contents under resting conditions. The concentrations of these constituents may show a 5- to 10-fold increase during and immediately after feeding. The analysis for [alpha]-amino N of portal and arterial blood taken from a sheep with a casein hydrolysate placed in its rumen suggested that amino acids are not absorbed from the organ. The rates of disappearance of NH3 and amino acids from the sheep rumen after the feeding of casein or casein hydrolysate were increased in the presence of carbohydrate. Much of the free [alpha]-amino N of whole rumen contents is associated with the microorganisms present. The time course of liberation of diffusible peptides and amino acids from casein, and the production of NH3 and volatile fatty acids was followed when the protein was incubated with washed suspensions of rumen organisms. The in vitro degradation of casein, bovine albumin, arachin, zein, wheat gluten and soya protein, by washed suspensions of rumen organisms from sheep fed on diets based on hay, casein and groundnut, was examined. Casein, arachin and soya protein were readily degraded, but bovine albumin, zein and wheat gluten were less extensively attacked.