Relationship of decreased caecal urease activity by dietary penicillin to nitrogen utilisation in chickens fed on a low protein diet plus urea.

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1. The relationship of the decreased caecal urease activity by dietary penicillin to nitrogen utilisation was assessed in chickens fed a low protein diet plus urea. 2. Dietary penicillin at 20 and 100 mg/kg decreased anaerobic bacteria counts, urease activity and ammonia concentration in caecal contents (P < 0.05, except for ammonia in the case of the 100 mg/kg penicillin diet). 3. The 20 mg/kg penicillin diets significantly increased the excretion of urea and total nitrogen (P < 0.05) and decreased ammonia excretion, and significantly reduced nitrogen retention (P < 0.05). The 100 mg/kg penicillin diet also resulted in similar but not significant changes, which tended to be less than those by the 20 mg/kg penicillin diet. 4. Ammonia, urea, glutamine and uric acid concentrations in blood, liver and kidney were unchanged by dietary penicillin. 5. It is concluded that caecal ammonia production from urea was closely correlated with nitrogen utilisation in chickens fed a low protein diet plus urea.