Degradation of maize protein in rumen contents. Influence of ammonia concentration.

1. The influence of ammonia concentration on the distribution of nitrogen derived from opaque-2 maize uniformly-labelled with 15N has been investigated during short-term in vitro incubation of bovine rumen contents. 2. Less 15N derived from maize was found in the non-protein-N (NPN) fraction during incubation without added NH3 than with added NH3, due entirely to differences in the amount of N derived from maize in the NH3 fraction. 3. From calculations based on the transfer of N derived from maize to the NPN pool and to a bacterial fraction, it was concluded that degradation of maize protein was not influenced by NH3 concentration within the examined limits. 4. The decrease in relative amount of N derived from maize in the NH3 fraction at low concentrations of NH3, together with evidence for an increased fractional turnover rate of NH3-N suggests that a deficient supply of NH3 is compensated for by increased catabolism of nitrogenous compounds derived from the rumen micro-organisms.