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Abstract
1. A study was carried out to investigate whether the back‐flow of urine into the caeca benefits the nitrogen economy of adult cockerels fed on a diet containing 100 g protein/kg and when dietary urea is absorbed, excreted into urine and utilised.
2. No significant effects of colostomy on nitrogen utilisation were observed in chickens fed on 100 g/kg protein diet, whereas colostomy was highly effective in decreasing it in chickens on a diet containing 50 g protein/kg plus urea (P< 0.05).
3. Nitrogen utilisation in conventional birds was significantly less when a diet of moderate protein content was fed than when a low protein diet plus urea was fed, but the opposite effect was seen with colostomised birds (P <0.05).
4. Colostomy increased urea excretion (nitrogen/kg body weight/day) from 4 to 9 mg in chickens fed on the moderate protein diet, but greatly, from 45 to 182 mg, in those fed on the low protein diet plus urea (P<0.05).
5. Blood urea concentration increased by about 20 mg per 100 ml in 3 h, a value which was maintained up to 6 h but which returned to the prefeeding concentration at 24 h; both control and colostomised chickens on the low protein diet plus urea responded similarly.
6. After feeding urea, half the daily excretion of urea was observed to occur within 6 and 9 h, respectively, in control and colostomised chickens. The excretion rate of urea (the peak occurred during 3.6 h in the colostomised and during 1.3 h in the control) was at least twice as high in colostomised as in normal birds 3 h postfeeding.
7. It is concluded that the caeca play a useful role in nitrogen economy of the protein‐depleted chicken, but not in the protein‐adequate chicken and that dietary urea degradation in the caeca occurs from 3 h after feeding.
