Performance of finishing beef steers in response to anabolic implant and zilpaterol hydrochloride supplementation.

Our objectives were to evaluate the dose/payout pattern of trenbolone acetate (TBA) and estradiol-1713 (E2) implants and feeding of zilpaterol hydrochloride (ZH) on performance and carcass characteristics of finishing beef steers. A randomized complete block design was used with a 3 × 2 factorial arrangement of treatments. British × Continental steers (n = 168; initial BW = 362 kg) were blocked by BW and allotted randomly to 42 pens (7 pens/treatment; 6 pens/ block; 4 steers/pen). The main effects of treatment were implant [no implant (NI); Revalor-S (REV-S; 120 mg of TBA + 24 mg of E2); and Revalor-XS (REV-X; 200 mg of TBA + 40 mg of E2)I and ZH (0 or 8.3 mg/ kg of DM for 20 d with a 3-d withdrawal before slaughter). Blocks were split into 2 groups, and block groups were fed for either 153 or 174 d. No implant × ZH interactions were noted for cumulative performance data. Overall, shrunk final BW (567, 606, and 624 kg for NI, REV-S, and REV-X, respectively), ADG (1.25, 1.51, and 1.60 kg), and G:F (0.14, 0.16, and 0.17) increased (P < 0.05) as TBA and E2 dose increased. Implanting increased (P < 0.05) DM1, but DM1 did' not differ (P > 0.10) between REV-S and REV-X (8.8 for NI vs. 9.4 kg/d for the 2 implants). From d ito 112 of the feeding period, implanting increased (P < 0.05) ADG and G:F, but REV-S and REV-X did not differ (P> 0.10). From d 112 to end, ADG increased by 19% (P < 0.05) and G:F was 18% greater (P < 0.05) for REV-X vs. REVS. Carcass-adjusted final BW (29-kg difference), ADG (0.2-kg/d difference), and G:F (0.02 difference) were increased (P < 0.05) by ZH, but daily DM1 was not affected by feeding ZH. Hot carcass weight was increased (P < 0.05) by ZH (19-kg difference) and implant, with REV-X resulting in the greatest response (HCW of 376 for NI vs. 404 and 419 kg for REV-S and REV-X, respectively; P < 0.05). An implant x ZH interaction (P = 0.05) occurred for dressing percent (DP). Without ZH, implanting increased DP, but DP did not differ (P > 0.10) between REV-X and REV-S. With ZH, REV-X increased (1.7%; P < 0.05) DP vs. NI and REV-S. Marbling score, 12th-rib fat, and KPH were not affected (P > 0.10) by implant or ZH. Overall, treatment increased steer performance and HCW in an additive fashion, suggesting different mechanisms of action for ZH and steroidal implants. In addition, a greater dose of TBA + E2 and extended payout improved steer performance and HCW. [ABSTRACT FROM AUTHOR]