Nitrogen Metabolism in the Ovine. I. Adjustment to a Urea-Rich Diet1

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Abstract
Experiments were conducted to investigate intraruminal and nitrogen balance changes occurring in lambs during adjustment to a urea-rich diet. In vitro rumen fermentation studies showed that the rate of ammonia assimilation by ruminal microorganisms was significantly greater using inocula from lambs that had been “adapted” to a urea-rich (3.5% urea) diet than with inocula from lambs fed a nonurea diet. However, ruminal ureolytic activity was higher in the case of lambs being fed the nonurea diet. Diet of donor animal did not significantly influence volatile fatty acid production in vitro. Intraruminal adjustments, as measured by in vitro criteria, were accomplished within 13 days following the introduction of the urea-rich diet. Rate of ammonia assimilation by ruminal microorganisms in vivo was determined from changes in ruminal ammonia concentration relative to polyethylene glycol, following an intraruminal infusion of a known amount of ammonia and polyethylene glycol. The maximum ability of ruminal microorganisms to assimilate ammonia was reached by the time the lambs had been 19 days on the urea-rich diet. Balance studies, conducted after two lambs had been consuming a 3.5% urea diet for 4, 20 and 41 days, revealed no significant difference in nitrogen balance. Similarly, urea recycling in these lambs did not appear to be influenced by the length of time the lambs had been consuming the urea-rich diet. Copyright © 1967. American Society of Animal Science . Copyright 1967 by American Society of Animal Science