PSV-28 Effects of various adaptation protocols on performance and carcass traits of Nellore bulls in a pasture-based finishing system.

Abstract This study aimed to evaluate the effects of various adaptation protocols for a pasture-based finishing system on the performance and carcass traits of Nellore bulls. Twenty-eight Nellore bulls were blocked according to initial body weight (BW) of 337 ± 3.98 kg and randomly assigned to one of four paddocks of Urochloa brizantha cv. Marandu (n = 7 per paddock). The paddocks covered an area of 2.5 ha, and the bulls were fed in individual Calan Gates bunks for a duration of 111 days. Experimental treatments included T1: a 21-day adaptation period with an initial concentrate ration supply of 0.5% of BW, increasing to 2.0% of BW by the end of 21 days (n = 10); T2: a 14-day adaptation period with an initial concentrate ration supply of 0.5% of BW, increasing to 2.0% of BW by the end of 14 days (n = 9); and T3: a 14-day adaptation period with an initial concentrate ration supply of 1.0% of BW, increasing to 2.0% of BW by the end of 14 days (n = 9). The BW assessment and average daily gain (ADG) were recorded every 28 days, except for the 27 days of the final period. The carcass ultrasound measurements evaluated marbling, rib-eye area, subcutaneous fat thickness, and biceps femoris fat thickness on days 0 and 111. At the end of the trial, bulls were slaughtered, and the hot carcass weight (HCW) and dressing percentage were recorded. Data were analyzed using PROC MIXED from SAS (SAS Inst., Inc., Cary, NC), and differences were considered significant at P ≤ 0.05. Overall, cattle that received an initial concentrate supply of 1.0% of BW during a 14-day adaptation period (T3) exhibited greater BW (547.16 kg), ADG (1.890 kg), HCW (302.56 kg), and biceps femoris fat thickness (6.67 mm) (P ≤ 0.05; Table 1). Furthermore, no effect of adaptation length or initial concentrate supply was observed on dressing percentage, marbling, loin eye area, and subcutaneous fat thickness after 111 days of trial (P > 0.05). Cattle in T1 and T2 did not differ from each other in any of the evaluated variables (P > 0.05). Adapting Nellore bulls to consume large amounts of a concentrate ration in a pasture-based finishing system over 14 days, starting with an initial concentrate supply of 1.0% of BW, improved performance and carcass traits. These findings indicate that a shorter adaptation period alongside a higher initial concentrate level can enhance growth performance and carcass weight in a pasture-based finishing system for Nellore bulls.