107 Effects of increasing doses of trenbolone acetate and estradiol on finishing phase growth performance and carcass trait responses in beef steers

Abstract

Abstract Continental × English beef steers (n = 240; allotment BW = 365 kg [SD 22.5]) were used in a randomized complete block design feedlot study to evaluate the effects of increasing doses of trenbolone acetate (TBA) and estradiol-17β (E2) on finishing phase growth performance and carcass trait responses. Steers were allotted to 30 concrete surface pens (n = 8 steers/pen) at the Ruminant Nutrition Center (RNC) in Brookings, SD 36 d prior to being implanted. Pens were assigned to 1 of 3 treatments: 1) No implant (NI), 2) Synovex Choice [100 mg TBA + 10 mg E2; CH], or 3) Synovex Plus [200 mg TBA + 20 mg E2; PL] on d 1. Cattle were fed for 124 d post-implantation. This experiment was part of a factorial experiment that included bedding application. No interactions between implant and bedding were detected (P ≥ 0.09). A common diet was fed that contained 2.09 Mcal/kg of NEm and 1.39 Mcal/kg of NEg and provided 30 g/ton of monensin sodium to diet DM. The first 6 pen replicates began on test 14 d prior to the last 4 pen replicates. Pen was the experimental unit; an α of 0.05 determined significance. There was a linear increase for both ADG (P = 0.01) and DMI (P = 0.02) with increasing doses of TBA and E2. There was a quadratic effect (P = 0.01) on carcass adjusted final BW. A quadratic effect on G:F was observed, increasing by 21.1%% and 19.5% for CH and PL respectively, compared to NI. No linear (P ≥ 0.14) or quadratic (P ≥ 0.40) effects were observed for dressing percentage, backfat, calculated yield grade, or marbling. A quadratic increase (P = 0.01) in HCW and a linear increase (P = 0.01) in REA was detected with increasing doses of TBA and E2. Combination TBA + E2 implants increased final BW, ADG, DMI, gain efficiency, HCW, and REA at equal BF accumulation without detriment to marbling score.