Effect of dietary protein levels on urinary excretion and plasma concentration of purine derivatives in crossbred bulls

The study evaluated the effect of different levels of crude protein (CP) intake on urinary excretion and plasma concentration of purine derivatives (PD) and creatinine in crossbred bulls. In a randomized block design, 15 growing crossbred bulls were fed a mixed diet (1:1) of wheat straw and concentrate mixture (with varying levels of CP) to meet their maintenance requirement for dry matter. A metabolism trial of ten days duration was conducted after 30 days of experimental feeding. The daily urinary excretion of allantoin and other PD decreased with the reduction in CP intake while creatinine excretion remained similar in groups fed at different levels. The microbial nitrogen (MN) supply calculated from the PD excreted in total urine (55.62 to 63.97 g/d) was higher at increased levels of CP intake. The concentration of PD in plasma reflected the differences in MN supply among groups fed at different levels of CP. The glomerular filtration rate (L/d) was unaffected by dietary levels of CP in crossbred bulls. The results of this study revealed that the plasma concentration of PD can be used as an index of microbial protein supply in crossbred bulls fed at different levels of CP.