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This experiment evaluated the dose and payout pattern of trenbolone acetate (TBA) and estradiol-17β (E2) on LM mRNA expression of adenosine monophosphate-activated protein kinase-ɑ (AMPK-ɑ), C/EBPβ, G protein-coupled receptor 41(GPR41), G protein-coupled receptor 43 (GPR43), PPARγ, and stearoyl CoA desaturase (SCD) in finishing feedlot steers as indicators of adipogenesis and marbling development. British · Continental steers (n = 168; 14 pens/treatment; initial BW = 362 kg) were used in a randomized complete block design. Treatments included: no implant (NI), Revalor-S (REV-S; 120 mg TBA + 24 mg E2), or Revalor-XS (REV-X; delayed release implant: 80 mg TBA + 16 mg E2 [uncoated], 120 mg TBA + 24 mg E2 [coated], 200 mg TBA + 40 mg E2 [total]). Steers were fed 1 time daily for an average of 164 d. The LM biopsies were collected (1 steer/pen) on d -1, 27, 55, and 111 relative to timing of implant. Total RNA was isolated from each sample and real-time quantitative PCR was used to measure quantity of AMPK-ɑ, C/EBPβ, GPR41, ,it, PPARγ, and SCD mRNA. No implant · day interactions were detected (P ≥ 0.19) in this experiment. Day impacted the mRNA expression of all adipogenic genes (P ≤ 0.02). The main effect of implant tended (P = 0.09) to influence expression of AMPK-ɑ, REV-X had an 8.8% increase over NI and an 18.7% increase over REV-S. Implant influenced (P = 0.03) mRNA expression of GPR41, expression of GPR41 for the REV-X treatment was not different (P > 0.10) from NI, and both were greater (P ≤ 0.05) than REV-S (1.13, 1.00, and 0.67 ± 0.224 arbitrary units) for REV-X, NI, and REV-S, respectively. Implant also influenced (P = 0.02) expression of GPR43, expression of GPR43 for REV-X was not different (P > 0.10) from NI, and both were greater (P ≤ 0.05) than REV-S (1.27, 1.07, and 0.72 ± 0.234 arbitrary units) for REV-X, NI, and REV-S, respectively. Implant influenced (P = 0.02) mRNA expression of PPARγ in LM tissue, expression of PPARγ for REV-X was not different (P > 0.10) from NI, and both were greater (P ≤ 0.05) than REV-S (1.09, 1.02, and 0.69 ± 0.195 arbitrary units) for REV-X, NI, and REV-S, respectively. The REV-X steers received the greatest anabolic dose of TBA + E2 without detriment to marbling scores. The increased mRNA expression of adipogenic genes for REV-X steers suggest that the delayed and gradual release of anabolic stimulants associated with REV-X might have mitigated decreases in marbling generally attributed to multiple combined TBA + E2 implants. [ABSTRACT FROM AUTHOR]

Twenty crossbred yearling steers (421 kg) were used to evaluate the effects of implanting with trenbolone acetate (TBA; 120 mg), estradiol-17β (E2; 25.7 mg), and a combination (120 mg of TBA and 24 mg of E2) on adipogenic and myogenic mRNA concentrations. Animals were blocked by BW and within each block were assigned to 1 of 4 treatments. Animals were housed and fed in individual pens with 5 animals per treatment. All animals were weighed weekly, and muscle biopsy samples were taken from the LM of each steer on d 0 (before implantation), 7, 14, and 28. Total RNA was isolated from each sample and real-time quantitative PCR was used to measure the quantity of C/EBPβ, PPARγ, stearoyl CoA desaturase (SCD), myogenin, and 3 isoforms of bovine myosin heavy chain (MHC) mRNA. Total BW gain from the 28-d period was adjusted to d 0 by use of covariant analysis, and steers in the implant groups tended (P = 0.09) to have increased BW gain compared with nonimplanted control steers. Analysis of the gene expression of MHC showed that neither implant nor day (P > 0.20) had a significant effect on the expression of type I or IIX MHC mRNA There was also no treatment effect (P > 0.20) on MHC-IIA and myogenin, but increasing days on feed increased (P = 0.05) the expression of MHC-IIA mRNA. Relative mRNA abundance of C/EBPβ, PPARγ, and SCD increased (P < 0.05) during days of feed but PPARγ decreased (P < 0.05) with the treatment of combined TBA/E2 implant. Results of this study indicate that implanting with TBA, E2, or both increased BW gain and decreased adipogenic gene expression of finishing steers without significantly affecting the concentration of type I, IIA, or IIX MHC mRNA. Increasing days on feed increased both MHC-IIA and adipogenic gene expression in bovine skeletal muscle biopsy samples. We conclude that administration of steroidal implants had no effect on the proportion of the 3 MHC mRNA isoforms but decreased C/EBPβ, PPARγ, and SCD mRNA in bovine skeletal muscle. [ABSTRACT FROM AUTHOR]