Interaction of Optaflexx® and terminal implant window on growth performance and carcass characteristics in heifers fed to harvest
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Objectives were to evaluate the interaction of ractopamine hydrochloride (OPT) and timing of terminal implant administration on growth performance, carcass characteristics, meat quality, serum metabolites and steroid hormones of finishing beef heifers. A 3x2 factorial randomized complete block design was used with 2 levels of OPT and 3 different durations of terminal implant windows for a total of 6 treatment groups with 9 replications. British x Continental heifers (n=216; 341.6 kg) were blocked by BW and randomly allotted to 54 pens (9 pens/treatment; 6 pens/block; 4 heifers/pen). The main effects of treatment were implant [TE-200 w/ Tylan (200 mg TBA + 24 mg E2) administered 140 d from slaughter (TI140); 100 d (TI100); and 60 d (TI60)] and OPT (0 or 200 mg/hd/d). Individual BW was collected at 0, 40, 80, 112, and 140 d and DMI recorded. No implant x OPT interactions were detected, so only main effects are reported. Average daily gain (0.14 kg/d difference), predicted carcass ADG (0.24 kg/d difference), HCW (5.6-kg difference) was increased (P<0.05) by OPT, but DMI was not affected. Heifers fed OPT tended (P≤0.09) to have a larger LMA (0.96 cm2 difference) and reduced marbling score. OPT supplementation decreased (P<0.05) Prime and Choice carcasses 16.5%. No affect of OPT was found on 12th-rib fat and KPH (P>0.10). Progesterone and blood urea nitrogen (BUN) were decreased (P<0.05) by OPT. No differences (P>0.10) in Warner Bratzler Shear Force (WBSF) were detected at d 3, 7, and 21 although at 14 d postmortem WBSF values of the OPT steaks were higher (0.45 kg; P<0.05). During the first 40 d on trial, ADG of the TI140 and TI100 groups was increased (P<0.05) compared to the TI60 (0.34 kg/d; 0.18 kg/d difference, respectively). From d 40-80, the TI100 had a higher ADG (P<0.05) than all other implant treatment 5 groups. TI60 had a higher ADG (P<0.05) than TI100 and TI140 from d 80-112. Predicted carcass ADG mirrored live ADG advantages (P<0.05). No differences (P>0.10) in DMI, final BW, carcass parameters, or WBSF were observed among the three implant strategies. Administering terminal implant decreased (P<0.05) BUN levels. Results from this study demonstrated that OPT, when fed to heifers, increased ADG, calculated carcass ADG, and HCW with minimal impact on carcass quality. Furthermore, this study indicated the duration of the terminal implant window did not affect overall performance, final BW, or carcass quality.