PLASMA-LEVEL, CLEARANCE AND RENAL EXCRETI ON OF ENDOGENOUS AND RUMINAL PURINES IN THE BOVINE

In 5 steers fitted with rumen cannulae the rumen was emptied after a p eriod of feeding maize whole crop silage + soybean meal, in order to e stimate by renal excretion of allantoin and uric acid the output of en dogenous purines. According to the time course of plasma concentration s of purines the collection period of urine was fixed to the interval of 10-34 h after rumen emptying. The excretion of purines in 24 hrs ur ine decreased from about 155 (fed state) to 69 mmol/d. Close correlati ons existed between plasma level and renal excretion of allantoin (r = 0.96) and of uric acid (r = 0.87). The renal excretion rates of purin es from endogenous and ruminal (exogenous) origines were estimated to 113 mumol/kg B.W. . d and 139 mumol/kg . d. The latter corresponded to 1.17 mmol/MJME or 18.5 mmol/kg DOM.