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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]