Rumen ammonia disappears from the rumen in different ways, such as incorporation of the nitrogen by the microbes, absorption through the rumen wall, and flushing to the omasum. Ammonia not taken up by the microbes is absorbed directly through the rumen wall. The rate of absorption is dependent on the pH of the rumen environment and the concentration of ammonia. Absorption is rapid at a pH of 6.5 or higher. It declines to nearly zero at a pH of 4.5.
Ammonia absorption increases as ruminal concentration increases.
Substitution of dietary nonprotein nitrogen, such as urea, for protein from plant and animal sources can reduce costs of protein supplementation. Urea is degraded by the microbes into ammonia, which can be used for microbial synthesis resulting in microbial protein. The microbes can also utilize nonprotein nitrogen in ensiled feeds and other feedstuffs. During the ensiling process, ammonia, amines, amides, and nitrates result from the degradation of protein and can be used as nitrogen sources by the rumen microbes. The ruminant animal relies upon microbial crude protein synthesized in the rumen and dietary protein which escapes digestion in the rumen for its supply of amino acids.