The utilization of non-protein nitrogen in the bovine rumen. 8. The nutritive value of the proteins of preparations of dried rumen bacteria, rumen protozoa and brewer's yeast for rats

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Abstract
A sample of dried bacteria (283 g.) was prepd. from bovine rumen liquid, by the method of McNaught et al.(1950). A sample of dried protozoa (447 g.) was prepd. from rumen contents by straining them through muslin, diluting the strained liquid with glucose solution, and allowing this liquid to settle at 39[degree]. The protozoal layer was separated by decantation. These prepns. when dried, contained 41.8% and 26.5% of crude protein, respectively. The biological value and true digestibility of the bacterial and protozoal protein were detd. at an 8% level of protein intake on groups of 12 young female rats by the balance-sheet method. Dried brewers'' yeast was also included in the trials. Biological values of 81, 80, and 72 were obtained for the proteins of bacteria, protozoa, and yeast, respectively. The corresponding values for true digestibility were 74, 91, and 84%. These results suggest that the conversion of bacterial or dietary protein into protozoal protein in the rumen is advantageous to the host animal.