Rumenal Flora Studies in the Sheep I. The Nutritive Value of Rumen Bacterial Protein

Abstract

SummaryTwo large satnples of "mixed" rumen bacteria, virtually free from protozoa and feed residues, were prepared from abattoir sheep, one from sheep coming from "green" feed conditions and the other from "dry"-fed sheep.The "true" digestibilities and biological values of the crude protein of these preparations were determined by nitrogen-balance method with young growing rats and compared with "standard" casein. The cyst ( e) ine and methionine contents of the rumen bacteria samples and of "whole" protein preparations made from them were also determined.The average "true" digestibilities of the protein of the "green"-fed and "dry"-fed rumen bacteria were found to be 62.1 and 64.8 respectively. These were not significantly different from each other but very much lower than that obtained for the casein, namely 101.2.The mean biological values found for the "dry"-fed rumen bacterial protein, the "green"-fed rumen bacterial protein, and the casein were 77.9, 79.1=), and 79.6 respectively, when fed as th~ sole source of nitrogen in the ration at levels of 9.2, 9.7, and 9.5 per cent. crude protein (N x 6.25).· The crude protein content of the "green"-fed· bacterial sample was 47.6 per cent. and of the "dry"-fed 50.9 per cent. on the dry basis. These samples and their protein preparations were found to be very similar in cystine content in relation to the total nitrogen present, but the former was appreciably richer in methionine.These findings were compared with those of other workers with similar material, with other microorganisms, and with other sources of protein, and are discussed in relation to the problem of the utilization of microbial protein by the ruminant.It is concluded that judged by results with growing rats, rumen bacterial protein must be r~garded as low in digestibility, relatively high in biological value, but mildly deficient in methionine.

Section A. Physiology of dairy cattle: The Biochemistry and Microbiology of the Rumen

“…It was found to be 80. This did not differ significantly from the biological value of rumen bacteria which was found in this same work to be 81, compared with 88 found by McNaught, Smith, Henry & Kon(90) and 79 found by Reed, Moir & Underwood (91). There was, however, a marked difference in the true digestibility of the nitrogen in the dried protozoa as compared with that in the dried bacteria, the values being 91 and 74% respectively.…”

Utilization of14C-labelledBacillus subtilisandEscherichia coliby sheep

“…Experiments have been done to determine the nutritive value of rumen bacteria (Johnson, Hamilton, Robinson & Garey, 1944;Reed, Moir & Underwood, 1949; McNaught, Smith, Henry & Kon, 1950) by feeding bacterial preparations to rats.…”

Influence of dietary nitrogen sources on amino acids in plasma and abomasal ingesta from sheep

“…The results of studies by Reed et al (1949) indicated that rumen bacterial methionine increased while the qrstine content did not change when samples from lambs fed "green" feed were caq)ared with the sangles from lambs fed "dry" feed. Weller (1957) studied the amino add com position of rumen microorganisms in the rumm fluid from sheep fed four different rations.…”

“…The total nitrogen content of a protozoa preparation containing mostly holotrichs as analyzed by Oxford (1951)# was observed to be from 1.1 to 1.6 per cent nitrogen, and a preparation containing both holotrichs and oligotrichs contained 3*5 per cent nitrogen. While, as McNaught et i^95^) observed, these differences may be due to a variation in protozoa carbohydrate storage, it is possible that there are differences in total nitrogen content between rumen protozoa genera and between rumen bac teria and rumen protozoa* Rumen bacteria appear to have a uniform total nitrogen content between seven and nine per cent (Johnson et al, 1944;Reed ^ al,, 1949;McNaught et ri., 1954;Abdoetjl., 1964 Heed eb (1949) found that the digestibility of rumen bacteria tqr rats was similar to sanqples of bacteria from sheep fed either "green" feed w "diy" feed, but the bacteria were much lover in digestibility in coB^arison to casein. These authors stated that rumen bacterial protein must be regarded as low in digestibility, relatively high In biological value, and mildly deficient in methionine.…”