Degradation of maize protein in rumen contents Influence of ammonia concentration

Abstract

1.The ineuCnce of ammonia concentration on the distribution of nitrogen derived from opaque-2 maize uniformly-labelled with 16N has been investigated during short-term in vitro incubation of bovine rumen contents.2. Less I6N derived from maize was found in the non-protein-N (NPN) fraction during incubation without added NH, than with added NH,, due entirely to differences in the amount of N derived from maize in the NH, 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 NH, concentration within the examined limits. 4.The decrease in relative amount of N derived from maize in the NH, fraction at low concentrations of NH,, together with evidence for an increased fractional turnover rate of NH,-N suggests that a deficient supply of NH, is compensated for by increased catabolism of nitrogenous compounds derived from the rumen micro-organisms.Since maize grain often accounts for a large part of the diet of beef cattle, information on the pattern of degradation of maize protein in rumen contents is important in order to improve the precision with which diets are compounded. In his review Chalupa (1978) only gave a gross estimate of 40% degradability for maize.Some evidence was obtained that protein catabolism in rumen contents may be increased at low concentrations of ammonia-nitrogen In order to elucidate whether the concentration of NH,, as an end-product of protein catabolism, af€ects the rate of breakdown of dietary protein, bovine rumen contents were incubated with maize, uniformly-labelled with 15N, in the presence and absence of added NH,. The results obtained suggest that an excess of NH, does not suppress hydrolysis of maize proteins within the limits studied. EXPERIMENTAL Maize labelled with 15NMaize (hybrid ZP-SK-72-0;) grown in two successive years on a plot fertilized with 15NH4, "No, and (15NH4),S0, respectivery was used in the experiment. The ears were dried at 60° for 24 h before separation of the grain. The total and non-protein-N (NPN) contents of the two samples are shown in Table 1 along with the values for lSN content. Samples of maize used for incubation were ground to pass a 1.5 mm screen.

Effect of roughage to concentrate ratio on ruminal fermentation and protein degradability in dairy cows

“…Perhaps catabolic processes in rumen bacteria are influenced by ammonia concentrations, and it might alter the rate of protein hydrolysis through end product inhibition. However, Nikolic & Filipovic (1981) were not able to demonstrate an effect of ammonia concentration on the degradation rate of maize CP.…”