Rumen ammonia concentration and ammonia assimilation by rumen microorganisms

Abstract

Pathways of ammonia assimilation were investigated at low and high rumen ammonia conditions by (1) measuring the specific activities (SA) of glutamate dehydrogenase (GDH), glutamine synthetase (GS) and glutamate synthase (GOGAT) in vivo and (2) comparing the rate of ('15)N-ammonia incorporated into amide-N and glutamate-N in vitro. The experimental procedure was a 2 x 2 Latin Square design. Two Angus steers with rumen cannulas were used as the donors of rumen microorganisms. The basel diet (B) contained 78% corn and 20% cottonseed hulls with 8.4% crude protein. Corn (2.3%) was replaced by urea in the basel + urea diet (U) which contained 15.3% crude protein. Intracellular and extracellular ammonia and amino acid concentrations were determined from the strained rumen liquor (SLR). Specific activities of both NAD and NADP linked GDH, GS, and GOGAT were measured in the crude enzyme extracts from mixed rumen bacteria. The SLR was incubated with ('15)(NH(,4))(,2)SO(,4). Media samples were then withdrawn at intervals thereafter and were measured for the amount of ('15)N-ammonia incorporated into amide-N and glutamate-N. ...