A Quantitative Study of Rumen Synthesis in the Bovine on Natural and Purified Rations II. Amino Acid Content of Mixed Rumen Proteins

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Abstract
Mixed rumen proteins obtained from 7 trials with rumen-fistulated calves maintained on a purified ration in which urea supplied the only essential source of dietary nitrogen, and from one calf fed a natural ration, were assayed by microbiological methods for the amino acids known to be essential for the rat. Quantitative evidence was obtained to show that rumen microorganisms can utilize urea nitrogen to synthesize amino acids. With the exception of histidine, the amino acid pattern of the mixed proteins in the ingesta of the calves on the purified ration was fundamentally similar to that found for the calf on the natural ration. Minimum molecular weights calculated for the mixed rumen proteins of the calves on the purified ration were in agreement with the values obtained for the mixed proteins in the ingesta of the calf on the natural ration.