An Overview on the Use of Urinary Purine Derivatives Excretion as a Method for Estimation of Rumen Microbial Protein Production in Swamp Buffaloes and Zebu Cattle

Abstract

Respond models based on urinary excretion of purine derivatives (PD) as an index to predict rumen microbial protein production have been developed for European cattle and sheep. However, there is evidence to suggest that those equations may not be applicable directly to tropical swamp buffaloes (Bubalus bubalis) and zebu Kedah-Kelantan (KK) cattle (Bos indicus). To establish similar equations for the above two species of ruminants, three studies were conducted. The first study examined the relationship between daily urinary PD excretion (Y, mmol) and duodenal purine bases (PB) (X, mmol). The relationships obtained were Y = 0.12 X + 12.78 (r 2 =0.45) for buffaloes and Y = 0.85 X + 7.15 (r 2 =0.62) for KK cattle, suggesting that 12 and 85% of the supplied exogenous purines were excreted in the urine of buffaloes and zebu cattle, respectively. In the second study, 8-[14C]-uric acid was used to test the hypothesis that the lower recovery of urinary PD in swamp buffaloes was due to their higher recycling of plasma PD as compared to KK cattle. Averaged non-renal loss of plasma [14C]-uric acid for swamp buffaloes and KK cattle did not differ significantly. A third study was conducted to examine whether the lower urinary PD excretion for buffaloes could be due to lower absorption in the small intestine as compared to cattle. The results indicated that apparent purine absorption rate for buffaloes as a percentage of disappearance in the first segment of small intestine was not significantly different from that of zebu cattle, even though a significantly larger quantity of digesta and PB was noted in the last 4 segments of the small intestine of buffaloes. The equation obtained in this study for zebu cattle is similar to those published for European cattle. Due to the extremely low recovery rate (12%), the proposed equation for buffaloes should be used with great caution.