| Summary: | Crossbred heifers ( = 64; animal was the experimental unit) were assigned to 1 of 8 treatments in a 4 × 2 factorial arrangement, with 4 treatment days-on-feed (DOF; 79, 100, 121, 142) and 2 levels of ractopamine hydrochloride (RAC) supplementation (0 or 300 mg × hd × d). At 24 h postmortem, carcass traits were determined by trained personnel and longissimus samples were removed for muscle fiber type analyses. Boneless strip loins (IMPS #180) were fabricated and vacuum-packaged at 24 h postmortem and aged for 21 d, cut into 2.54 cm thick steaks, then frozen for no longer than 6 mo. After thawing for 24 h, Warner-Bratzler shear force (WBSF) and trained sensory panel analyses were conducted. Marbling was greater ( < 0.05) for control (CON; 0 mg x hd-1 x d-1 ractopamine hydrochloride) heifers than RAC heifers fed for either 79 or 100 d, but lower ( < 0.05) for CON heifers than RAC heifers fed for either 121 or 142 DOF. Feeding RAC had no effect ( > 0.05) on carcass traits, muscle fiber histology, or meat quality. The addition of RAC had no effect ( > 0.05) on Warner-Bratzler shear force. Feeding RAC had no negative impacts on carcass traits or meat quality and actually improved marbling scores in longer-fed heifers.
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