Urinary excretion of purine derivatives and plasma allantoin level in sheep and goats during fasting

The relationship between blood plasma level and urinary excretion of allantoin (AN) was examined in sheep and goats during fasting to investigate the possible use of purine derivatives (PD) in urine and/or plasma for estimating the microbial protein production in the rumen, and the further digestion in the lower guts of ruminants. Urinary AN excretion decreased markedly during fasting (0.13 mmol/kgW0.75 per day), although urinary levels of other PD, hypoxanthine + xanthine and uric acid did not differ irrespective of the feeding condition, that is, feeding, fasting and refeeding in both species. The AN concentration in blood plasma also decreased drastically in the starvation period, and was suddenly increased on refeeding in sheep and goats, and these phenomena were very similar to those of urinary AN excretion. Therefore, there was a high positive correlation between plasma AN level and urinary AN excretion, and the coefficient of correlation was statistically significant (P < 0.01). These results clearly indicate that changes in urinary AN reflect change in plasma AN, which is induced by the catabolism of purine base in the body.