The effect of limit feeding and delaying implanting until d-64 of the finishing period on growth performance and carcass characteristics of backgrounded beef steers

Abstract

The objective of this study was to determine the effects of feed restriction and implant timing on growth and carcass characteristics of finishing beef steers. Charolais cross steers (n = 232; initial shrunk body weight [SBW] = 478 ± 27.4 kg) were allocated into 24 open dirt lot pens (8 steers/pen) and 8 partially covered pens (5 steers/pen). Pens were randomly assigned to one of four treatments in a 2 × 2 factorial arrangement of implant and diet strategy. Implant treatments consisted of administration of 200 mg trenbolone acetate and 20 mg estradiol – 17β (Revalor 200; Merck Animal Health, Rahway, NJ) on d-1 (INI) or d-64 (DEL). Diet treatments were ad libitum feeding throughout the feeding period (ADL) or restriction to 92% of ad libitum for 63 d, followed by ad libitum feeding (RES). The RES pens were offered 92% of the intake of the ADL pens within the same implant strategy and block. Data were analyzed using the MIXED procedure in SAS 9.4, with the GLIMMIX procedure used for categorical distributions. Diet, implant strategy, and their interaction were fixed effects, and block was the random effect. There was only one interaction effect (P = 0.04) of gain to feed (G:F) from d 64 to 85. From d 1 to 63, dry matter intake (DMI) and average daily gain (ADG) were greater for the INI and ADL groups (P < 0.01) while G:F was only greater in the INI group (P < 0.01). By d 64, SBW was greater in the INI and ADL groups (P < 0.01). During d 64 to 142, DMI did not differ between treatments (P ≥ 0.23), however, DMI as a percentage of BW was greater for RES (P = 0.05). The DEL group had greater ADG and G:F (P < 0.01). Cumulatively, DMI was greater in the INI and ADL groups (P ≤ 0.03) but final BW, ADG, and G:F did not differ between the implant or feeding management treatments (P ≥ 0.12). Carcass-adjusted final BW (HCW/0.625) and ADG were also similar between treatments (P ≥ 0.66), while G:F was only greater in the DEL group (P = 0.04). Hot carcass weight and marbling score did not differ (P ≥ 0.43). Rib fat was greater in the INI group while ribeye area was greater in the DEL group (P ≤ 0.01). Performance calculated energetics did not differ (P ≥ 0.10). Yield grade distribution shifted towards more Yield Grades 1 and 2 in the DEL group (P = 0.02). Restricting feed intake during the initial 63-d resulted in reduced DMI but similar final SBW and HCW. Delaying implanting had similar results, however rib fat was decreased, and ribeye area was increased.