ARS | Publication request: METABOLISM OF NITROGEN-CONTAINING COMPOUNDS

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 29, 1996
Publication Date: N/A

Technical Abstract: The way in which the rumen has evolved as the first digestive organ potentially affords ruminants an efficiency of protein nutrition that is not available to non-ruminant herbivores. Protein is synthesized in the gut in the form of rumen microorganisms. The necessary energy is derived from plant polysaccharides such as cellulose, and the nitrogen is derived from ammonia and amino acids in the rumen. The energy and nitrogen sources can therefore be substrates of little value to most non-ruminants. The benefit derived from the rumen fermentation varies according to the diet. Cows can maintain unimpaired milk production on diets lacking protein with cellulose as principal carbon source and urea as the main nitrogenous nutrient. Yet, especially with intensive production systems, the nitrogen metabolism of rumen microorganisms is usually regarded as being inefficient. Dietary protein is broken down much too rapidly relative to the breakdown of the energy-containing plant fibre, excessive ammonia production results, and the biological value of the dietary protein is severely reduced. The objectives of research in this field have therefore been twofold. One is to capitalize on the microbial capacity to form protein from ammonia by feeding non-protein nitrogen (NPN). The other is to minimize protein breakdown in the rumen, and thereby to increase the 'bypass' or 'escape' protein (i.e., dietary protein unaffected by passage through the rumen) reaching the lower tract. This chapter reviews the information available on the microbial transformation of nitrogen compounds in the rumen and discusses the impact of ruminal digestion on the protein nutrition of the host animal.