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Angus × Simmental steers (n = 210; initial BW 314 ± 11 kg) were separated into heavy and light BW blocks and allotted evenly by BW to 6 treatments (3 heavy and 2 light pens per treatment) to determine the effect of supplemental vitamin D3: 0 IU (no D), 250,000 IU for 165 d (long-term D), or 5 × 10(6) IU for 10 d (short-term D) on performance, carcass traits, vitamin D metabolites, and meat tenderness in steers fed either 0 (NZ) or 8.38 mg/kg zilpaterol hydrochloride (ZH) daily for 21 d. Placebo or ZH was added to the diet 24 d, and short-term D was added 13 d before slaughter. Vitamin D3, ZH, and placebo were all removed from the diet 3 d before slaughter. Steers fed ZH tended to have improved overall G:F compared with steers not fed ZH (P0.09). Overall performance was not affected by long-term D, with or without ZH (P = 0.11) compared with no D, with or without ZH. Short-term D decreased final BW, ADG, and G:F (P = 0.04) compared with no D, when ZH was not fed. Zilpaterol hydrochloride increased HCW, dressing percentage, and LM area (P0.01); and decreased fat thickness, yield grade, and marbling (P0.03). Carcass traits were not impacted by long-term D without ZH (P0.13), but long-term D with ZH decreased percentage KPH (P0.02). Compared with no D, short-term D tended to decrease HCW (P0.07), decreased fat thickness (P0.01), and tended to increase dressing percentage (P0.10) when ZH was not fed, yet did not impact carcass traits when ZH was fed (P0.13). Feeding ZH tended to decrease (P0.09) LM 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. The long-term D treatment increased LM vitamin D3 and 25-hydroxyvitamin D3 (25OHD3) 18- and 5-fold, respectively, when ZH was not fed (P0.04) and increased LM 25OHD3 by 4-fold when ZH was fed (P0.01). Short-term D increased LM vitamin D3 and 25OHD3 by 52- and 9-fold, respectively, when ZH was not fed (P0.01), and by 24- and 9-fold, respectively, when ZH was fed (P0.01). Also, short-term D increased LM 1,25(OH)2D3 by 2-fold (P0.04) when ZH was fed. Warner-Bratzler shear force (WBSF) was greater for ZH steaks than non-ZH steaks at 7, 14, and 21 d postmortem aging (P0.01). Vitamin D did not reduce WBSF (P = 0.18). When ZH was fed, long-term D tended to increase WBSF in steaks aged 21 d (P = 0.06). In conclusion, ZH improved carcass leanness and decreased tenderness, and vitamin D feeding increased vitamin D3 metabolites in LM, but did not improve tenderness in steers fed ZH. |
