Evaluation of Long Acting Combination Implants Containing Trenbolone Acetate and Estradiol-17β on Live Performance, Carcass Traits, and Sera Metabolites in Finishing Steers

Crossbred beef steers (n = 240; 12 pens/treatment; initial BW = 305 ± 17.7 kg) were used in a randomized block design feedlot study to evaluate the influence of long acting trenbolone acetate (TBA) and estradiol-17β (E₂) implants (Merck Animal Health, Madison, NJ) on gain performance, carcass traits, and sera metabolites. The five treatments were no implant (NI), Revalor-XR on d 0 [200 mg TBA + 20 mg E₂ (coated); XR], Revalor-XS on d 0 [200 mg TBA + 40 mg E₂ (total): 80 mg TBA + 16 mg E₂ (uncoated) and 120 mg TBA + 24 mg E₂ (coated); XS], Revalor-200 on d 0 [200 mg TBA + 20 mg E₂ (uncoated); E200], or Revalor-200 on d 70 (D200). Interim BW and blood were collected on d 0, 14, 35, 70, 105, 140, and 175 prior to feeding, and on d 213 prior to shipping. Following a 24 h clot at 4°C, sera was harvested to quantify circulating E₂, IGF-I, NEFA, serum urea-N (SUN) and 17β-trenbolone (17β-TbOH). Implanted steers had greater (P ≤ 0.05) ADG, G:F, and final BW than NI controls. Implants increased (P < 0.05) HCW by 8%, 366 vs. 391, 414, 380, and 396 ± 6.4 kg, for NI vs. XR, XS, E200, and D200, respectively. The greatest (P ≤ 0.05) dressing percentage, yield grade, and calculated empty body fat occurred in XS, which had greater (P < 0.05) rib fat than NI, XR, and D200. Marbling scores in NI were greater (P < 0.05) than E200 and D200; XR and XS were intermediate (P > 0.10), not differing from others. An implant × day interaction (P ≤ 0.01) was noted for circulating E₂, IGF-I, SUN, and 17β-TbOH. Implanted steers had elevated (P ≤ 0.05) serum E₂, IGF-I, and 17β-TbOH, and decreased (P < 0.05) SUN following implantation compared to NI controls. Serum NEFA differed (P < 0.01) over time, but did not differ (P > 0.10) due to implant treatment. These data indicated that the polymer coating applied to the XR implant delayed release of anabolic constituents congruently to D200. The greatest dose of E₂, contained in XS, provided improvements in gain and carcass weight without detriment to marbling scores compared to NI.