Effects of non-protein nitrogen on buffel grass fiber and ruminal bacterial composition in sheep

•The bacterial community does not vary with the increased availability of ruminal ammonia in sheep fed a basal diet of buffel grass hay.•The concentration from 8.34 to 8.66% crude protein maximized the use of buffel grass.•Buffel grass hay is a good food source associated with nitrogen supplementation for sheep. This study aimed to evaluate different concentrations of non-protein nitrogen (NPN) ruminal infusion in sheep fed buffel grass hay on nutrient intake and digestibility, ruminal parameters, nitrogen balance, and rumen bacterial composition. Five rumen-fistulated adult wethers, weighing 58 ± 5.1 kg were distributed according to a 5 × 5 Latin square design. The control treatment consisted of a 5.5% crude protein (CP) buffel grass hay basal diet only, while the other four treatments consisted of the addition, via ruminal infusion, of increasing amounts of NPN to gradually raise the level of CP in the basal diet (7.44, 9.39, 11.33 and 13.27% CP). There was a quadratic effect for the intake of dry matter (DM), organic matter (OM), CP, ether extract (EE) and neutral detergent fiber (NDF). Values of pH, volatile fatty acids, microbial protein, microbial efficiency and digestibility coefficients were not affected by CP levels in basal diet. On the other hand, there was a linear effect for the concentrations of ammonia nitrogen (NNH3) and nitrogen (N) in urine, and a quadratic effect for ingested and excreted N in feces, as well as for N balance. There was no effect of the different CP levels on the ruminal microbial composition. While the 5.5% CP basal diet provided sufficient NPN supply for the maintenance of ruminal bacterial activity, increased CP concentrations from 7.34 to 8.66% by means of ruminal infusion with NPM optimized the utilization of buffel grass nutrients by sheep.