The effect of dietary energy source on nitrogen metabolism in the rumen of sheep

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Abstract
Seven isonitrogenous diets were prepared containing soybean meal and dried grass either unsupplemented, or supplemented with wheat starch or paper or equal mixtures of both. The diets were allocated according to a balanced incomplete block design to 7 Clun Forest wether sheep, each fitted with a re-entrant duodenal cannula. After each sheep had received a diet for 6 days, daily samples of digesta were collected automatically for the next 3 days. The amounts of dry matter, gross energy and major nitrogenous components consumed in the diet, passing into the duodenum and excreted in the urine and feces were determined. A novel method was applied to estimate the proportion of the total amino acids passing into the duodenum which was of microbial origin. The amounts of microbial total amino acids synthesized were compared with the amounts of energy disappearing in the rumen for each of the 7 diets tested. For the starch- and paper-containing diets an average of 14.7 g microbial total amino acd passed into the duodenum per MJ energy disappearing in the rumen: for the diets containing either paper or starch alone the mean value, 6.1 g/MJ, was significantly lower (P < 0.05). The energy released from a mixture of starch and paper was utilized more efficiently for microbial protein synthesis than when the energy was provided by supplements of either paper or starch along.