The influence of levels of protein and starch in rations of sheep on the utilization of protein

It has recently been well established that the overall utilization of protein by ruminants represents the result of two opposing processes of ammonia utilization: part of the ammonia produced by the decomposition of food protein may be excreted as urea in the urine, and thus lost to the animal, and part may be built into valuable microbial protein and utilized by the host animal.However, only a few assessments of the nutritive value of proteins supplied in different types of feeds have been conducted on the basis of the metabolic fate of proteins in the ruminant.It was found in this laboratory (Tagari, Ascarelli & Bondi, 1962) that a decrease in solubility of different protein feeds as a result of heat treatment, such as the toasting of soya-bean meal, is accompanied by improved utilization (cf.Chalmers, 1961 b ; Sherrod & Tillman, 1962).The reason given for this was that highly soluble proteins such as those of untoasted soya-bean meal are degraded in the rumen to NH, at a rate too rapid for efficient utilization.Two further aspects of this problem are considered in this paper.Supplying excess protein to cattle is typical of the feeding practice prevailing in many countries.This is so during the greater part of the year in Israel, where protein-rich feeds, such as leguminous forage are more plentiful during the winter than are carbohydrate-rich foods.Most practical rations that could be formulated to meet the energy requirements of ruminants for that season would of necessity include a considerable excess of protein.The influence of giving a surplus of proteins on the metabolic reactions occurring in the rumen has therefore been studied.