SummaryThe data are presented from a replicated feeding trial designed to determine the influence of different sources of nitrogen, fed at a constant level, upon the nitrogen balances and numbers and types of ruminal microorganisms in growing Iambs. Six Merino Iambs were fed a basal ration of oaten chaff and wheaten grain supplemented with six sources of nitrogen: linseed meal, subterranean clover seed, whole powdered egg, casein, urea, and urea plus methionine. In each diet the test nitrogen contributed 40 per cent. of the total nitrogen and the crude protein (N X 6.25) content of the whole diet was very close to 10 per cent. All diets were very similar in crude fibre and gross energy content. Additional data for certain of these diets were obtained with seven mature Merino wethers.The mean biological values of the nitrogen of the different rations as fed to the Iambs were: linseed 79.7 ± 2.59; subterranean clover seed 83.0 ± 3.43; egg 86.7 ± 4.28; casein 82.0 ± 6.05; urea 68.6 ± 1.52; urea plus methionine 75.2 ± 1.48. The biological value of the nitrogen of the whole powdered egg ration was significantly greater (P < 0.01) than that of linseed, of linseed significantly greater (P < 0.01) than that of urea plus methionine, and this significantly greater (P < 0.01) than that of urea. The values for the casein and subterranean clover seed rations were significantly greater than that of the urea (P < 0.01) and urea plus methionine (P < 0.05) rations but were not significantly different from each other nor from the other protein nitrogen sources. The mean concentrations of ruminal bacteria on the different rations were found to be: linseed 23.9 ± 8.46; subterranean clover seed 25.2 ± 10.5; egg 41.2 ± 5.23; casein 42.8 ± 9.94; urea 17.7 ± 2.09; urea plus methionine 43.7 ± 9.12 million per cu. mm. The ruminal bacterial numbers were highly significantly greater (P < 0.01) for the. egg, casein, and urea plus methionine diets than for the linseed, subterranean clover seed, and urea diets. It is concluded that: (i) Different sources of nitrogen can vary markedly in their biological value, i.e. capacity to promote nitrogen retention in growing Iambs.(ii) Different sources of nitrogen can vary markedly in their capacity to promote bacterial growth in the rumen of both growing Iambs and mature sheep.(iii) The value of methionine, as a supplement to urea, in improving nitrogen retention in growing Iambs is due largely to its stimulating effect on bacterial growth in the rumen, thus increasing the amount of bacterial protein available to the host. The numbers of ruminal protozoa were found to be highly variable and to bear no obvious relationship to the diets fed.Some of the morphological characteristics of the rumina I bacteria on the various diets are presented and discussed.
Caecectomized and sham-operated rats were fed a laboratory chow ad libitum and the effects of caecectomy on the digestibility of the food were studied. Compared with sham-operated controls, caecectomized rats showed a decrease in apparent digestibility of organic matter from 77·8 to 73 ·0%, of crude protein from 83·0 to 79·4%, and of 'carbohydrate' from 74·6 to 69·0%. However, faecal water content increased from 41·6 to 54·8 %. StCr-labelled EDTA was excreted faster in the faeces after caecectomy. The colon partly adapted to the loss of caecal mucosa by increased length and thus mucosal surface area.In a second concurrent experiment the effect of caecectomy on the apparent digestibility of food during food restriction was studied. Six caecectomized rats, comparable in all respects to those used in the first study, were fed the laboratory chow ad libitum for 3 weeks. They were then fed submaintenance amounts of food to achieve body weight losses of 40-50 % and to maintain these low weights for 4 weeks. Finally, they were again fed ad libitum for 3 weeks. During the period of restriction the apparent digestibility of organic matter increased from 72·7 to 75·4 %. This was largely due to the increased apparent digestibility of crude protein which rose from 78·4 to 81·9%. Digestibility coefficients returned to control values immediately upon refeeding ad libitum.
Minimum transit time through the alimentary tract of young adult female rats fed a stock diet adlibitum was reduced from 6� 6 � 0�4 h for sham-operated rats to 5�0 � 0�3 h for caecectomized rats, but there was no effect on transit time of digesta along the small intestine. Caecectomy decreased the apparent digestibility of crude protein, soluble carbohydrate, cellulose and hemicellulose. Digestibility of lipid was not affected. However, caecectomized rats did not increase their dry matter intakes to compensate for the reduced digestible energy intakes.
Data are presented from a replicated feeding trial with sheep, designed to determine the influence of varying dietary intakes of starch and protein upon digestibility, protein utilization, and the numbers and types of "free" bacteria in the rumen.
Sheep were fed on either lucerne chaff, high wheat grain, or high maize grain rations. Analyses were made on digesta from the rumen and large intestines of cannulated and slaughtered animals. The results for the large intestine showed that, when equal quantities of dry matter are given, the composition of the ration can affect the pH, the water content, and the total dry matter of the digesta; diet can also affect the total quantities of volatile fatty acid and ammonia in the organ.The proportions of the individual volatile fatty acids in the caecal fluid were not affected by the different diets fed in this experiment. The data did not suggest any consistent pattern in the pH or in the concentrations of ammonia and volatile fatty acid in the caecal fluid during the 24 hr between feeds.
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