Animal Science Department


Date of this Version



The Professional Animal Scientist 2 5 ( 2009 ):580–585


Copyright 2009 American Registry of Professional Animal Scientists


Two commercial feedlot experiments were conducted to compare performance and carcass characteristics of feedlot heifers and steers using 2 implant strategies. In Exp. 1, heifers (n = 1,124; initial BW = 279 ± 5 kg) were administered either Revalor-IH [Intervet/ Schering Plough Animal Health, DeSoto, KS; 8 mg of estradiol (E2) and 80 mg of trenbolone acetate (TA)] or Synovex-H (Fort Dodge Animal Health, Overland Park, KS; 20 mg of estradiol benzoate and 200 mg of testosterone propionate) at initial processing, with both treatment groups receiving Revalor-200 (20 mg E2 and 200 mg TA) as the common terminal implant 81 d (range 69 to 85 d) before slaughter. In Exp. 2, steers (n = 1,066; initial BW = 269 ± 2 kg) were administered either Revalor-IS (16 mg E2 and 80 mg TA) or Synovex-S (Fort Dodge Animal Health; 20 mg estradiol benzoate and 200 mg progesterone) at initial processing, with both treatment groups receiving Revalor-S (24 mg E2 and 120 mg TA) as a common terminal implant an average of 78 d (range 71 to 84 d) before slaughter. Implanting heifers initially with Revalor-IH improved G:F (P = 0.01) and ADG (P = 0.05) compared with heifers implanted initially with Synovex-H. In addition, Revalor-IH implanted heifers tended to have greater (P = 0.07) marbling scores, and 58% more carcasses (P = 0.02) achieved the upper two-thirds Choice category with no differences observed in USDA YG. Implanting steers initially with Revalor-IS tended to increase hot carcass weight (P = 0.07) and carcass-adjusted final BW (P = 0.07) compared with steers implanted initially with Synovex-S. However, implanting steers initially with Revalor-IS had no effect on performance or carcass characteristics compared with an initial implant of Synovex-S. Overall, moderatedose E2-TA initial implants can improve both G:F and marbling scores in heifers. In steers, moderate-dose E2-TA initial implants may improve hot carcass weight and carcass-adjusted final BW but may have no impact on carcass characteristics.