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

Abstract

Earlier papers (cf. Pearson & Smith, 1943) in this series described the considerable protein synthesis which occurs when rumen liquid, obtained from a bullock with a permanent fistula, is incubated in vitro with non-protein nitrogen and readily available carbohydrate. Smith & Baker (1944) later corre- lated this protein synthesis with increase in numbers of iodophilic bacteria. Subsequent work showed that the protein of a dried preparation of rumen bacteria, approximately 40 % of which had been synthesized during incubation in vitro, had, when tested in rats, the high biological value of 88 (McNaught, Smith, Henry A Kon, 1950). Its true digestibility was, however, only 73%. In reviewing the subject of nitrogen metabolism in the rumen, McNaught & Smith (1947) pointed out that, al- though the power of the rumen protozoa to syn- thesize protein had not been specifically demon- strated (Schmid, 1939; Smith & Baker, 1944), it was possible that they served a useful purpose by assimilating bacterial protein and thus rendering it more available .to the host. The observation of Usuelli & Fiorini (1938), that growth of chicks was progressively improved by additions to their diet of bacteria and protozoa from the rumen of sheep, is in accord with the hypothesis that rumen protozoa contribute to .the nutrition of the host animal.