Effects of different backgrounding supplementation on performance and rumen morphometrics of Nellore bulls finished on tropical pasture

ABSTRACT This study aimed to evaluate the effects of backgrounding supplementation, by increasing the levels of energy-protein supplements during the growing phase on the performance and rumen morphometrics of Nellore bulls intensively finished on pasture. Ninety-six Nellore bulls were blocked according to initial body weight (BW) of 385.6 ± 7.3 kg and randomly assigned to one of 24 paddocks of Urochloa brizantha cv. 'Piata' (four animals/paddock). The animals were supplemented during the growing phase as follows: (1) energy-protein supplementation at 0.05% BW, (2) energy-protein supplement at 0.1% of BW, (3) energy-protein supplement at 0.3% BW, and (4) energy-protein supplement at 0.5% of BW for 112 days. Thereafter, all bulls were fed a concentrate at 1.5% BW for 84 days in the finishing phase on pasture. The supplement intake, BW assessment, and average daily gain (ADG) were recorded every 28 days. At the end of the trial, the hot carcass weight was recorded. Rumen and cecum were scored, and morphometric parameters evaluated. Dry matter intake during both the growing and finishing phases increased with higher levels of supplementation (P<0.01). There was a quadratic effect (P = 0.03) during the growing phase, with bulls supplemented at 0.3% and 0.5% of BW showing greater ADG; however, during the finishing phase, a linear decrease effect was observed (P = 0.01). A linear increase effect was observed for final BW, with bulls consuming 0.05% of BW being lighter. In addition, as the level of supplementation increased, hot carcass weight also increased (P<0.01), while no effects were observed on rumen and cecum parameters. Providing an energy-protein supplement during the growing phase is an effective nutritional strategy. Higher levels of supplementation result in greater final body weight at the end of the growing phase and, consequently, improved performance during the finishing phase of Nellore bulls finished on pasture.