65 Effect of two different implant programs on growth performance and carcass characteristics in beef steers fed to three differing harvest endpoints

Abstract Two implant programs (Merck Animal Health, DeSoto, KS and Zoetis, Parsippany, NJ) and 3 d on feed (DOF) endpoints were used to evaluate growth performance and carcass characteristics of finishing beef steers. Beef steers n = 480; initial body weight (BW) = 402; SEM = 2.4 kg were assigned to treatment pens (10 steers/pen) with pen (n = 48 pens total) as the experimental unit. Treatments were arranged as a 2 x 3 factorial including implant program: 1) a single Revalor-XS (200 mg trenbolone acetate and 40 mg estradiol-17β total) on d 0 (XS) compared with 2) Synovex-Choice (100 mg trenbolone acetate and 14 mg estradiol benzoate) on d 0 and re-implanted with a Synovex-ONE Feedlot (200 mg trenbolone acetate and 28 mg estradiol benzoate) 70 d later (CHSOF) and harvest endpoint: 1) 162 DOF, 2) 183 DOF, or 3) 204 DOF. Both implant groups were removed from their pens on the day of reimplantation. Data were analyzed as a RCBD. Final BW was calculated as HCW/0.625. An implant × DOF (P ≤ 0.04) interaction was noted for gain to feed ratio (G:F), REA, final BW adjusted to 28% estimated empty body fatness (AFBW), and USDA quality grade distribution, a tendency for an interaction was observed for final BW, average daily gain (ADG), HCW, and dressing percentage (P ≤ 0.09), no other interactions were noted for any traits evaluated (P ≥ 0.17). Steers from CHSOF/162 had increased G:F by 4.1 to 6.5% compared with others (P ≤ 0.05). Steers from XS/204 had greater REA by 3% to 10% (P ≤ 0.05) compared with all other treatments and greater AFBW by 3% to 7% (P ≤ 0.05), compared with all other treatments except CHSOF/204. Steers from XS had a greater proportion of carcasses grading USDA Prime at 162 and 183 DOF compared with CHSOF. As a result of increased DOF, the XS/204 and CHSOF/204 steers had greater final BW and HCW compared with all other treatments (P ≤ 0.05), steers from XS/183 had greater HCW than XS/162 and CHSOF/162; however, CHSOF/183 did not differ from CHSOF/162 (P ≤ 0.05). Steers from CHSOF/162 had greater ADG by 5.8% compared with CHSOF/183 (P = 0.05), while all others were intermediate. Dressing percentage was the greatest for XS/204 and least for CHSOF/183 (P ≤ 0.05). Cattle from XS had increased (P 0.01) DMI by 2.6%. As DOF increased, carcass-adjusted final BW increased while ADG decreased (linear; P = 0.05). As DOF increased, REA and AFBW increased (P 0.01). Increasing DOF, increased (P 0.01) USDA yield grade 4 and 5 carcasses and decreased yield grade 2 and 3 carcasses. Implant strategy had a marginal influence on growth performance and carcass characteristics; however, as DOF increased carcass weights, rib fat, and ribeye area increased.