Comparison of Urea and Protein Meals as Nitrogen Sources for Rumen Micro-Organisms: Urea Utilization and Cellulose Digestion

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Abstract
In vitro experiments comparing urea with soybean, linseed, cotton-seed and corn gluten meals indicated the superiority of urea as a nitrogen source in promoting cellulose digestion by rumen micro-organisms. The utilization of urea in 1:1 mixtures with various feed proteins was very efficient, and its presence in such mixtures improved cellulose digestion above that observed with the feed proteins alone. The data indicate that the availability of nitrogen from protein or non-protein sources is of great importance to efficient cellulose digestion. An increase in the level of urea used as a sole source of nitrogen resulted in an increase in cellulose digestion as well as in the amount of urea utilized. A level of urea was reached above which the concentration of free ammonia apparently inhibited both urea utilization and cellulose digestion.