LAUSR

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 on sera metabolite responses, gene expression, and immunohistochemical analyses of the Longissimus muscle. Performance data were analyzed as a randomized complete block design and all other data were analyzed as repeated measures for a completely randomized design. 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 muscle (LM) biopsies, blood, and BW were collected before feeding on day (d) 0, 14, 28, 56, 84, 112, and 133, with final BW being captured on d 140. Genes of interest were 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). An α of 0.10 determined significance for performance and sera data; α of 0.05 was used for gene and histology data. No performance differences (P ≥ 0.10) were detected. An implant × d 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 across d of the study, meaning sera metabolites are not altered with time on feed. An implant × d interaction was detected for myogenic factor 5 (Myf-5) positive cells and proportions of MHCIIX. In LM, CI had greater (P < 0.10) IGF-I in LM over NI. Coated implant increased (P < 0.05) GPER1 expression, as well as, GPER1 semi quantitative scores over NI and NC. An implant × d interaction (P ≤ 0.05) for estrogen and androgen receptor positive nuclei was detected; implants had increased (P ≤ 0.05) estrogen and androgen receptor positive nuclei compared to NI. Coated implants increase genes associated with muscle tissue growth.