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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]

Our objectives were to determine the effects of zilpaterol hydrochloride (ZH) and the release rate of trenbolone acetate and estradiol-17ß on Warner-Bratzler shear force (WBSF) and slice shear force (SSF) of longissimus lumborum (LL) and the WBSF of gluteus medius (GM) and psoas major (PM) in response to various aging periods. British × Continental steers (n = 168) were assigned to treatments in a 3 × 2 factorial. The main effects of treatment were implant [no implant (NI); Revalor-S (REV-S), Revalor-XS (REV-XS)] and ZH (0 or 8.3 mg/kg of DM for 20 d). Harvest group was included as a random effect to account for the variation in days on feed (153 or 174 d). Loins (n = 96) were fabricated to obtain strip loin, top sirloin butt, and tenderloin subprimals. Five 2.54-cm steaks were cut from each subprimal and assigned to 1 of 5 aging periods (7, 14, 21, 28, or 35 d postmortem). Feeding ZH increased (P < 0.01) LL WBSF and SSF values at each aging period compared to controls. Implanting increased (P < 0.05) LL WBSF values at 14 and 21 d, but did not affect LL SSF values (P > 0.05). Only REV-S increased WBSF values at 28 and 35 d compared to NI or REV-XS. The percentage of LL steaks with a WBSF value < 4.6 kg did not differ (P > 0.05) between ZH supplementation or implant strategy at any aging period, and by d 28 over 99% of LL steaks registered WBSF values < 4.6 kg. Feeding ZH increased (P < 0.05) GM WBSF values only on d 21. Implant had no effect (P > 0.05) on GM WBSF values. The percentage of GM steaks with a WBSF value < 4.6 kg did not differ (P > 0.05) between ZH supplementation or implant strategy at any aging period. Neither ZH nor implant strategy affected PM WBSF values (P > 0.05). All PM WBSF values were < 4.6 kg on d 7. The results of this study indicated feeding ZH increased WBSF and SSF of LL steaks, regardless of aging period; however, the percentage of steaks with WBSF < 4.6 kg did not differ due to ZH or implant. Implanting increased LL WBSF, but not SSF values. These results showed although differences existed between implanting, as well as ZH supplementation of British × Continental steers, 99% of LL steaks were classified as tender based on WBSF values by extending aging to 28 d postmortem. It should be noted that 21.2% of 7 d, 13.8% of 14 d, and 17.3% of 21 d ZH steaks had WBSF values > 4.6 kg, but 0% of non-supplemented steaks were > 4.6 kg at these aging periods. However, because ZH and implants can increase retail yield of valuable subprimals such as the tenderloin, considerable value could be captured through ZH supplementation with anabolic implants since shear force was not affected in PM steaks. [ABSTRACT FROM AUTHOR]

We previously showed that a combined trenbolone acetate (TBA)/estradiol-17β (E2) implant significantly increases IGF-I mRNA levels in the LM of feedlot steers by 28 d after implantation. Here we compare the effects of E2 (25.7 mg), TBA (120 mg), and combined TBA (120 mg)/E2 (24 mg) implants on IGF-I, ICF-I receptor (IGFR-1), estrogen receptor (ER)-α and androgen receptor (AR) mRNA levels in the LM of steers. Twenty yearling crossbred steers with an average initial BW of 421.1 ± 3.6 kg were stratified by BW and randomly assigned to 1 of 4 treatments: 1) nonimplanted, control; 2) implanted with TBA and E2; 3) implanted with E2; or 4) implanted with TBA. Steers were weighed weekly starting on d 0, and muscle biopsy samples were taken from each steer on d 0 (before implantation), 7, 14, and 28. Ribonucleic acid was prepared from each sample and real-time reverse transcription-PCR was used to determine the levels of IGF-I, IGFR-1, ER-α, and AR mRNA. Body weight of implanted steers, adjusted by using d-0 BW as a covariant, tended (P = 0.09) to be greater than that of control steers. On d 7 and 28, IGF-I mRNA levels were greater (58 and 78%, respectively; P < 0.009) in E2-implanted animals than in control steers. Similarly, on d 28 the LM IGF-I mRNA level was 65% greater (P = 0.017) in TBA/E2-implanted steers than in control animals. In contrast, the TBA implant did not increase (P = 0.99) LM IGF-I mRNA levels after 28 d of implantation. Muscle IGFR-1, AR, and ER-α mRNA levels were not different (P > 0.47) in any of the treated groups compared with the control group. These data suggest that E2 is responsible for the increased muscle ICF-I mRNA level observed in steers implanted with a combined TBA/E2 implant. [ABSTRACT FROM AUTHOR]