227 Evaluation of reimplant timing with Revalor-200 on steer performance and carcass characteristics
Abstract The objective of this study was to evaluate the optimal time to reimplant following an initial implant on performance and carcass characteristics when steers were fed for 180 d. Crossbred steers (n = 800; initial BW = 330 ± 25 kg) were utilized in a generalized randomized block design and assigned randomly to pen, and pen assigned randomly to one of five treatments. Treatments included 5 different days on terminal (DOT) implant (160, 120, 100, 80 or 40 DOT). All steers were given an initial implant (80 mg trenbolone acetate (TBA) + 16 mg estradiol; Revalor-IS) on d 1. Terminal implant consisted of 200 mg TBA + 20 mg estradiol (Revalor-200). Dry matter intake was the least for 40 DOT (P ≤ 0.04), with no differences between the other treatments (P ≥ 0.11). Carcass-adjusted final BW responded quadratically (P = 0.03) with 100 DOT having the greatest final BW but was not different from 120 DOT (P = 0.82). Carcass-adjusted ADG and G:F responded quadratically (P = 0.02 and P < 0.01, respectively). When solved for the first derivative, carcass-adjusted ADG and G:F were maximized at 99 and 87 DOT, respectively. However, there was less than a 2% difference in carcass-adjusted ADG and G:F between 80 and 120 DOT. Hot carcass weight responded quadratically (P = 0.03), with the greatest HCW at 100 DOT. Solving for the first derivative, HCW was optimized at 104 DOT. There were no differences in back fat, marbling, or yield grade (P ≥ 0.27). Overall, administering an initial implant followed by a terminal implant 85 to 105 d prior to harvest increased gain, efficiency, and HCW in steers when fed for 180 d. Minimal changes in performance and carcass characteristics when steers are reimplanted 80 to 120 d prior to harvest suggests flexibility in reimplanting windows.