Ruminal nitrogen metabolism and the passage of amino acids to the duodenum in sheep receiving diets containing hay and concentrates in various proportions

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Abstract

Abstract Three sheep fitted with rumen cannulas and three sheep fitted with duodenal re‐entrant cannulas in addition to rumen cannulas were given, in successive periods, 700 g d −1 of five diets consisting of chopped hay and a concentrate mixture of rolled barley and flaked maize (50:50) in the ratios of 1:0, 5:2, 3:4, 1:6, and 0:1. For bacteria isolated from the rumen of sheep fitted with rumen cannulas only, there were no significant differences in either the content of nitrogen in their dry matter or in the amino acid composition, but the content of α‐ϵ‐diaminopimelic acid varied significantly ( P < 0.05) between diets, mean values ranging from 39 to 50 kg −1 nitrogen. As the proportion of concentrate in the diet increased, the intake of nitrogen was progressively reduced from 11.9 to 9.8 g d −1 and this was accompanied by an increase in the amount of organic matter apparently digested in the rumen, from 296 to 402 g d −1 . But there were no significant differences between diets in either the ruminal concentration of ammonia‐nitrogen (mean values varied from 78 to 96 mg litre −1 ) or in the duodenal passage of total nitrogen, which ranged from 12.1 to 14.7 g d −1 with a peak value for the 5:2 diet. Rates of synthesis of bacterial protein in the rumen were 186, 228, 124 and 94 g crude protein per kg organic matter apparently digested in the rumen for the 1:0, 5:2, 3:4, 1:6 and 0:1 diets respectively, the rates for the 1:6 and 0:1 diets being significantly ( P < 0.05) lower than those for the other diets. The 0:1 diet was associated with a low proportion, 0.5, of bacterial protein in the duodenal crude protein and it is suggested that with this diet, protozoal protein made an appreciable contribution to the crude protein passing from the rumen.

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