Evaluation of coated and non-coated steroidal implants in beef steers: Live performance, carcass traits, and biological responses



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In Experiment 1) 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 coated 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 (non-coated) and 120 mg TBA + 24 mg E2 (coated); XS], Revalor-200 on d 0 [200 mg TBA + 20 mg E2 (non-coated); 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; steers in XR and XS were intermediate (P > 0.10), not differing from NI, E200, or D200. 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) sera 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 steroidal hormones congruently to D200, with no negative impact on marbling. The greatest dose of E2, contained in XS, provided improvements in gain and carcass weight without detriment to marbling scores compared to NI. In Experiment 2) Predominately Angus steers (n = 24; initial BW = 435 ± 28.3 kg) were used to evaluate non-coated and coated implants containing equal amounts of trenbolone acetate (TBA; 200 mg) and estradiol benzoate (EB; 28 mg) in finishing steers. Treatments were no implant (NI), non-coated (NC; Synovex-PLUS; Zoetis, Parsippany, NJ) and coated (CI; Synovex-One Feedlot) implant. There were 2 pen replicates per treatment (n = 4 steers/pen). Longissimus (LM) biopsies, blood, and BW were collected before feeding on d 0, 14, 28, 56, 84, 112, and 133. Androgen receptor (AR), estrogen receptor-α (ER-α), G protein-coupled estrogen receptor 1 (GPER1), IGF-I, and IGF-I receptor (IGF-IR) mRNA expression in LM was determined by RT-qPCR using two housekeeping genes. Sera was analyzed for estradiol-17β (E2),17β-trenbolone (TbOH), IGF-I, NEFA, and urea-N (SUN). Data were analyzed as repeated measures for a completely randomized design; α of 0.10 determined significance. An implant × day interaction (P ≤ 0.10) for E2, IGF-I, and SUN was detected; implants elevated (P ≤ 0.10) E2, 17β-TbOH, and IGF-I; and decreased SUN. No implant × day interaction was detected (P ≥ 0.20) for any genes, or histological analysis of satellite cell populations, except for Myf-5 positive cells (implant × day interaction; P < 0.10). Coated implant increased (P < 0.10) GPER1 expression, as well as, GPER1 semi quantitative scores over NI and NC. In LM, CI had greater (P < 0.10) IGF-I in LM over NI. An implant × day interaction (P ≤ 0.10) for estrogen and androgen receptor positive nuclei was detected; implants had increased (P ≤ 0.10) estrogen and androgen receptor positive nuclei compared to NI. Differing payout characteristics did not influence AR, ER-α or IGF-IR. Coated implants altered GPER1; increasing IGF-I in LM that is critical for proliferation and differentiation of satellite cells. The potential to further enhance lean accretion in steers, fed longer periods, is improved by CI as compared to NI.



Beef, Estradiol-17β, IGF-I, Implant, Steer, Trenbolone