Excretion of purine derivatives in cows: endogenous contribution and recovery of exogenous purine bases

Two dry cows fitted with simple cannula in the rumen and duodenum, and fed with a mixed diet (straw:barley, 50:50), were used to determine endogenous losses and response of urinary purine derivatives (PDs) to duodenally infus ed yeast-RNA. Duodenal flow of purine bases (PBs) was determined by a dual marker system, and N-15 was infused continuously into the rumen to label mi crobial PBs. The isotope dilution of urinary PDs in relation to duodenal PB s confirmed the presence of an endogenous fraction (236 mu mol/kg LW0.75) b igger than in sheep and lower than values estimated in cows with impaired r umen fermentation. Excretion of PDs increased linearly in response to incre mental supply of PBs with an equimolar recovery of 0.84 mol/mol. However, n et recovery of duodenal PBs was 0.67 for the basal diet and 0.65, 0.90, 0.7 9 and 0.82 for the four levels of PB infusion, it is suggested that differe nces in digestibility between yeast-RNA and duodenal PBs might explain diff erences in recovery estimations. (C) 2001 Elsevier Science B.V. All rights reserved.