Purine Derivative Excretion and Recovery of ¹⁴C-Uric Acid in Urine of Ongole Cattle Given Different Levels of Feed Intake

Abstract

The microbial protein supply to ruminants can be estimated based on the amount of purine derivatives (PD) excreted in the urine. Two experiments were conducted to evaluate the purine derivatives method for Ongole cattle. In the first experiment, 4 four-year old male Ongole cattle (Bos indicus) were used to calibrate the PD technique using the most common locally available feed at four levels of intake (95, 80, 60 and 40% of voluntary intake). The diet consisted of king grass and rice bran (70:30 on DM basis). The cattle at the level of 95% intake were injected with [¹⁴C]-uric acid in a single dose to define the renal:non-renal partitioning ratio of plasma PD excreted in the urine. The results showed that PD excretion responded positively to the level of feed intake. The relative proportion of urinary allantoin and uric acid to PD excretion was 0.87 and 0.13 respectively. The proportion of urea N to total N ranged from 83 to 93%. The glomerular filtration rate and tubular load of PD increased due to the increasing level of feed intake. Nitrogen balance became negative when the level of feed intake decreased to 60%. The proportion of plasma PD excreted in the urine was 0.67.