Effect of tannin extract associated with two levels of non-protein nitrogen in the supplement on performance, ruminal parameters, and microbial diversity of grazing Nellore cattle during the growing phase at dry season

The objective of this study was to evaluate the effects of tannin extracts (TE) with two levels of nonprotein nitrogen in protein-energy supplements on the intake, apparent total tract digestibility, ruminal and blood parameters, rumen microbial diversity, and performance of grazing Nellore cattle during the growing phase in the dry season. In experiment 1 (Exp. 1), eight ruminally cannulated Nellore steers [293 +/-& nbsp;5.6 kg of body weight (BW)] were used in a double 4 x 4 Latin square design in a 2 x 2 factorial arrangement. In experiment 2 (Exp. 2), sixty-four Nellore bulls (294 +/- 15.2 kg of BW; blocked by initial BW) at eighteen months old were distributed in 16 paddocks in a 2 x 2 factorial arrangement as follows: urea at 30 g/kg (UR3) or 50 g/kg (UR5) as feed supplement without TE or with TE (7 g/kg as feed supplement). The animals were fed daily with protein-energy supplements at 3 g/kg of BW, and the paddocks consisted of Urochloa brizantha cv. Marandu grass. In Exp. 1, the total intake, forage intake, and apparent total tract digestibility were similar among the treatments. A TE x Urea interaction trend was observed for supplement intake in kg/day (P = 0.05) or % of BW (P = 0.09), with lower intake in UR3 without TE than UR3 with TE while no effect of TE at UR5. The NH3-N concentration was higher in steers supplemented with TE (P = 0.02). The NH3-N concentration was higher in animals fed UR5 than in those fed UR3 at 6 h after supplementation (P < 0.01). Animals supplemented with TE had a lower Simpson index (P = 0.01), lower total ruminal ciliate protozoa counts (P = 0.02), and higher richness estimators (P < 0.05). In Exp. 2, the animal performance was not influenced by the Urea, TE or their interaction (P >=& nbsp;0.230). The use of 30 or 50 g/kg urea in the protein-energy supplements during the dry season does not alter animal performance, metabolic changes make it flexible. TE use alters the microbial population but does not affect performance. Thus, the use of supplements with a higher nonprotein nitrogen amount is a useful strategy for improving the cost-benefit ratio in protein-energy supplements for beef cattle during the dry season. However, higher blood urea correlates with increased N excretion in the environment, and further studies are needed to verify these possible impacts. (AU)