158 Effect of Weaning Strategy and Backgrounding Length on Growth Performance, Carcass Characteristics, and Mrna Expression in the Longissimus Muscle of Beef Steers

Abstract

Abstract This study aimed to investigate the effect of the weaning strategy (WS; early, at 130 ± 21 d vs normal, at 187 ± 20 d) and backgrounding length (BGL; short vs long) on growth performance, carcass characteristics, and relative mRNA expression in the longissimus muscle (LM) of beef steers. Angus × SimAngus-crossbred steers [n = 120; body weight (BW) = 130 ± 11.2 kg] were used in randomized complete block design. Steer calves were blocked by age and BW and randomly assigned to 1 of 4 treatments (2×2 factorial arrangement). Treatments consisted of early or normal weaned steers with either a short or a long BGL. Early weaned steers were ad libitum-fed a grain-based diet for 49 d until nursing calves were normally weaned. Subsequently, steers were ad libitum-fed a hay-based diet for 214 d or a concentrates-based diet for 95 d, for the long or the short BGL, respectively. Steers were finished on a high grain diet until harvested at a common 12th rib fat thickness. Longissimus muscle biopsies were performed on days 1, 57, 112, 168, 255. Data were analyzed using PROC MIXED in SAS. Early weaned steers were heavier (P < 0.01; Table 1) at the beginning of the backgrounding and finishing period. When the finishing phase began, steers with a long BGL were heavier (P < 0.01; Table 1) than steers with a short BGL. There was a WS × BGL interaction (P = 0.01; Table 1) for final BW, where normal weaned steers with a long BGL were the heaviest among treatments. In the finishing phase, steers with a long BGL had greater DMI and ADG, but lower G:F (P < 0.01; Table 1) than steers with a short BGL. There was WS × BGL interaction (P = 0.03; Table 1) for days on feed (DOF) in the finishing phase, where early weaned steers with a short BGL required less days on DOF to reach harvesting target than the remaining treatments. No interactions or treatment effects (P ≥ 0.11; Table 2) were detected for marbling score (MS). For the mRNA expression of ZFP423, a WS × d interaction was detected (P < 0.01; Figure 1). Day×WS interaction (P < 0.01) was observed for ZFP423 mRNA expression, early weaned steers showed a greater expression at d 112 and a decreased expression at d 255. For DLK1, a BGL×d interaction occurred (P < 0.01; Figure 2). In d 57 steers with a short BGL presented a greater DLK1 mRNA expression than steers with long BGL, whereas in d 255, this was inverted. Overall, data from this experiment does not support the implementation of different WS and BGL as a method to improve the MS of beef carcasses.