Effect of feeding graded levels of undegraded dietary protein on the flow rate of microbial nitrogen, dietary non-ammonia nitrogen and alpa amino nitrogen at abomasum in crossbred calves

Abstract

Crossbred calves (4) each fitted with a rumen and an abomasal cannula were fed on 4 types of concentrates, varying in CP content (g/kg) and also the RDP: UDP ratio, viz. 234 and 79: 21 for Tâ‚, 210 and 68: 32 for Tâ‚‚ 184 and 59: 41 for T₃ and 159 and 48: 52 for Tâ‚„ groups along with wheat straw ad lib. and 2 kg green maize, in a 4 x 4 latin-square design. Concentrates Tâ‚ contained 20% higher CP, Tâ‚‚ a normal level, whereas the concentrates T₃ and Tâ‚„ contained 10 and 20% less CP than the standard recommendations. Chromium mordanted GNC was used as digesta marker for measuring digesta flow rate and RNA was used as a microbial marker for measuring the microbial flow rate. The flow rates of NAN and alpha-AAN (g/day) at the abomasum were similar on all 4 diets, although the N intake (g/day) decreased from T1 to T4. The lower N intake was offset by higher UDP intake from T1 to T4 as reflected in the similar NAN flow rate. Fractionation of total NAN showed a significant increase in dietary plus endogenous NAN flow (g/day) from T1 to T4 and a corresponding decrease in microbial NAN flow from T1 to T4. As a percentage of N inlake, the alpha-AAN showed an increasing trend from high CP low UDP diet (T1) to the low CP high UDP diet (T4).