Microbial Growth Dependence on Ammonia Nitrogen in the Bovine Rumen: A Quantitative Study

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Abstract
A. dry cow was fed rations of either alfalfa or alfalfa-barley pellets in two equal portions daily. Whole rumen digesta samples were withdrawn at intervals just before feeding and 2, 3, 4, 6, and 8 hours after feeding. In each of these samples rates of ammonia nitrogen in- corporation into ruminal microbes and rates of volatile fatty acid production were determined in vitro. Weights of digesta in the rumen were determined by emptying. Data from these measurements enabled estimation of daily yields of microbial cells dependent on ammonia nitrogen and of moles of adenosine triphosphate (ATP) potentially formed during fermentation of: 1,124.7 g microbial cells and 56 moles ATP pyrophosphate bonds (,~ P); and, 710.6 g cells and 34 moles ATP (~ P) for the two rations. These estimates indi- cate that under the experimental conditions and range of nitrogen intake investigated, microbial growth derived from ammonia N was independent of nitrogen intake and dependent upon energy intake. Compari- son of the estimates of microbial growth dependent on ammonia N in this study with estimates of total microbial growth in the literature of 15 to 33 g per 100 g of digestible organic matter fed, indicated that between 42 and 100% of microbial nitrogen could be derived from ammonia nitrogen.