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Effects of dietary urea on nitrogen balance and excretion of urinary nitrogenous compounds were investigated using cockerels with an artificial anus. In the experiment 1, the cockerels were fed a casein diet containing 0, 0.5, 1.0 and 2.0% urea. In the experiments 2 and 3, they received corn-soybean meal diets. The diet containing 6% of soybean meal was added with 0, 0.44, 0.88 and 1.76% urea in Experiment 2, and the 18% soybean meal diet was added with 0, 0.44 and 0.88% urea in Experiment 3. The latter diets were restrictedly fed to the birds so as to that the birds consumed the same amount of nitrogen as that of the urea-free basal diet.In the birds fed the casein diet, the fecal excretion of nitrogen was about 10% of the nitrogen intake regardless of the amount of dietary urea. The urinary excretion of nitrogen increased and the nitrogen balance decreased proportionally with an increase in dietary urea level. Urinary uric acid was increased by supplementation of urea, but no further increase was found when the diet was added with 1.0% and 2.0% urea. This suggests that bacterial urease activity in the digestive tract is low, and consequently plasma ammonia for the synthesis of uric acid does not increase. The excretion of urea increased with an increase in urea intake. It is considered that excess urea is absorbed from the digestive tract without decomposition and most of absorbed urea are excreted into urine directly. When urea was added to the 6% soybean meal diet, more nitrogen was excreted in feces compared to that in the casein diets. The urinary excretion of nitrogen increased with the increasing level of dietary urea and the increased amount was nearly equivalent to the urea nitrogen intake. No remarkable changes on nitrogen balance were observed in the birds fed urea. In cockerels fed the 18% soybean meal diets, fecal nitrogen was decreased by supplementation of urea. Although nitrogen intake derived from the basal diet was low in the birds fed the urea diets, urinary nitrogen excretion remarkably increased. The increase in dietary urea level raised the excretion of urinary urea and uric acid.It is considered that urea added to a casein diet or a corn-soybean meal diet is not only unutilizable by cockerels but promotes the excretion of the other nitrogen compounds especially uric acid and lowers the biological value of protein.
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