Nitrogen metabolism in sheep. II.* The flow of amino acids into the duodenum from dietary and microbial sources

Abstract

Sheep were fitted with re-entrant cannulae in the duodenum and offered diets supplying 1.4, about 16, or 30 g nitrogen per day from lucerne, casein, or wheat gluten. There were two levels of metabolizable energy in the diets.

The flow of α-amino nitrogen into the duodenum was less than the dietary intake for sheep on all diets except the one supplying 1.4 g nitrogen per day. The flow of most individual amino acids into the duodenum was less than the dietary intake. The flow of glutamic acid and histidine was only 14 and 15 % of the dietary intake in the sheep given 30 g nitrogen per day. However, in the sheep offered wheat gluten the flow of lysine to the duodenum was greater than the dietary intake. Some other dietary differences in amino acid concentration were reflected in the rumen and duodenal contents, but the differences were diminished. The flow of methionine and cystine into the duodenum ranged from only 3.1 to 15.8 mmoles per 24 hr.

The percentage of microbial protein in the rumen and duodenal contents was estimated by the incorporation of ³⁵S into cystine, and was found to range from 43 to 97 %. The percentage of microbial protein was inversely related to the dietary nitrogen intake and was dependent on both the dietary source of nitrogen and the intake of metabolizable energy.

An average of 6.2% of the ³⁵S continuously infused into the rumen as sulphate could be recovered at the duodenum.

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*Part I, Aust. J. Agric. Res., 23: 1059 (1972).