Nitrogen Metabolism of Ruminant Animals: Historical Perspective, Current Understanding and Future Implications

Nitrogen metabolism of ruminant animals has been the subject of thousands of research publications. Study of ruminai and intestinal function continues. The quantitative and qualitative importance of ruminai microbes as a source of protein have become apparent in many trials, and factors controlling microbial protein synthesis or growth of microbes as well as ruminai degradation of dietary protein have been explored. Information on the supply side of the protein ledger (ruminai synthesis, bypass or escape of dietary protein; intestinal digestion) exceeds current knowledge of quantitative needs for amino acids. Descriptive models of N metabolism have evolved that amalgamate current concepts. With future amendments, these systems should prove useful in diet formulation to more fully utilize ruminai fermentation and increase productive efficiency of ruminant animals. Expanding knowledge of ruminai N metabolism will permit greater control and manipulation of the processes of ruminai fermentation and postruminal digestion.