The application of modern concepts of ruminant protein nutrition to sheep-production systems

New systems for estimating the requirements of ruminants for dietary protein involve separate estimates of the extent to which microbial and undegraded dietary protein meet the animal's net requirements for amino acids. The paper provides a brief review of the factors influencing both the synthesis of microbial protein and the amounts of dietary protein that escape the rumen undegraded. Although quantitative data on many of these factors are now emerging, the extensive nature of most sheep-production systems makes their application in a precise quantitative manner difficult. It is suggested that considerable improvements in production could be achieved by using the principles in a qualitative sense. For low-producing animals such as dry ewes, pregnant ewes up to a few weeks before lambing, and ‘store’ lambs, microbial protein will meet the animal's net requirements for amino-acid nitrogen provided that the animals have not been previously subjected to a specific protein deficiency. In contrast, the maximal yield of microbial protein will not meet the net requirements of high-producing animals, such as young, fast-growing lambs, and ewes in the final few weeks of pregnancy and during early lactation. These animals require protein supplements which at least in part escape degradation in the rumen.