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, GPR43, 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.
- Beef steers
- Trenbolone acetate