Effects of implants on daily gains of steers wintered on dormant native tallgrass prairie, subsequent performance, and carcass characteristics

Fall-weaned crossbred steer calves (n = 300; 184 +/- 2.9 kg) received eithe r no implant (Control) or were implanted with Synovex(R)-C (SC = 10 mg estr adiol benzoate + 100 mg progesterone), Synovex(R)-S (SS = 20 mg estradiol b enzoate + 200 mg progesterone), or Revalor(R)-G (RG = 8 mg estradiol-17 bet a + 40 mg trenbolone acetate) to determine the effects of implants on weigh t gain during winter grazing on dormant tallgrass prairie, subsequent grazi ng and finishing performance, and carcass characteristics. Steers grazed tw o dormant tallgrass prairie pastures from October 16, 1996, until March 29, 1997 (164 d), and received 1.36 kg/d of a 25% CP supplement that supplied 100 mg of monensin/steer. Following winter grazing, all steers were implant ed with Ralgro(R) (36 mg zeranol) and grazed a common tallgrass prairie pas ture until July 17 (110 d). After summer grazing, all steers were implanted with Revalor-S(R) (24 mg estradiol-17 beta + 120 mg trenbolone acetate), a nd winter implant treatment groups were equally allotted to four feedlot pe ns. Steers were harvested November 17, 1997, after a 123-d finishing period . Daily gains during the winter grazing phase averaged .28, .32,.32, or .35 kg/d, respectively, for Control, SC, SS, or RG steers and were greater (P < .01) for implanted steers than for Controls. Summer daily gains were simi lar (1.05 +/- .016 kg/d; P greater than or equal to .61) for all treatment groups. Feedlot daily gains were also similar (1.67 +/- .034 kg/d; P greate r than or equal to .21), with implanted steers weighing 14 kg more than Con trol steers (P = .05) at harvest, despite similar management during summer grazing and feedlot phases. Control steers tended (P = .06) to have lower y ield grades. There were no differences (P = .99) in marbling between implan ted and nonimplanted steers. Steers implanted during the wintering phase ha d increased skeletal and overall (P < .01) carcass maturities compared with nonimplanted steers, which resulted in more "B" and "C" maturity carcasses . Because carcass maturity score affects quality grade, the increased matur ities of implanted steers resulted in a $9.04 decrease in carcass value/100 kg (P < .01) compared with Controls. The results of this study indicate th at growth-promoting implants are efficacious for cattle wintered on dormant native range despite low daily gains. This increased weight is maintained through the summer grazing and feedlot phases; however, the benefit of the increased weight may be offset by decreased carcass quality grade and value due to increased carcass maturity.