Evaluation of coated steroidal combination implants on feedlot performance and carcass characteristics of beef heifers fed for constant or varying days on feed

Abstract

Two experiments evaluated the effects of delayed, long-lasting implant strategies for finishing heifers fed for constant or varying days on feed. In Exp. 1, heifers (n = 500; initial BW = 280 ± 21 kg) were allotted randomly to 1 of 5 treatments, including no implant (CON), Revalor-XH on d 1 (XH), Revalor-200 on d 1 (E200), Revalor-XR on d 1 (XR), or Revalor-200 on d 70 (D200). All implants contained 200 mg of trenbolone acetate and 20 mg of estradiol. In Exp. 2, 720 heifers (initial BW = 281 ± 10 kg) were assigned randomly to treatments in a 3 × 4 factorial arrangement, with 3 implant treatments [no implant (NCON), Revalor-200 on d 1 and 100 (PCON), or Revalor-XH on d 1 (XH)] and 4 serial slaughter dates following 151, 165, 179, or 193 d on feed. In Exp. 1, implanted heifers were heavier, gained more, and were more efficient (P ≤ 0.03) compared with CON heifers, but no differences were observed among implant treatments (P ≥ 0.21) over the 198-d finishing trial. Implanted heifers had greater hot carcass weight but lower marbling scores compared with CON heifers (P ≤ 0.04). In Exp. 2, there were no serial slaughter × implant treatment interactions for growth performance (P ≥ 0.23) or carcass characteristics (P ≥ 0.31). Final BW, fat thickness, and numerical YG increased linearly (P < 0.01), whereas ADG (P = 0.01) and G:F (P = 0.02) decreased linearly, with increasing days on feed. Hot carcass weight was increased by implanting strategy and increasing days on feed, but aggressive initial implants did not improve performance.