Metabolism of nitrogen-containing compounds

The way in which the rumen has evolved as their 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. Even more important, however, is the direct availability of that microbial protein for digestion and absorption by the host animal. Herbivores which employ hind-gut fermentation can only achieve the same efficiency of microbial protein utilization by coprophagy. In contrast, microbial protein is generally the ruminant’s principal source of amino acids.