Effects of supplementing zinc or chromium to finishing steers fed ractopamine hydrochloride on growth performance, carcass characteristics, and meat quality

Objectives were to determine the effects of feeding ractopamine hydrochloride (RAC) with zinc (Zn) and chromium (Cr) on feedlot growth performance, carcass characteristics, and meat quality. Steers (n = 179; initial BW = 533 +/- 94 kg) were blocked by BW and allotted to 30 pens, and pens were randomly assigned 1 of 5 treatments: (1) control (CONT), (2) RAC only (RO), (3) RAC + Zn (RZ), (4) RAC + Cr (RC), or (5) RAC + Zn + Cr (RZC). Trace minerals were fed from d 0 to 63 to target 1 g of Zn/steer.d(-1) (KemTRACE Zn; Kemin Industries, Inc., Des Moines, IA) and 3 mg Cr/steer.d(-1) (KemTRACE Chromium; Kemin Industries, Inc.) for Zn and Cr treatments, respectively. Dry-rolled corn, 0.605 kg/steer, was removed from the diet and 400 mg RAC, per 0.605 kg of ground corn carrier, was top dressed per steer immediately following feed delivery to pens fed RAC. There were no effects (P >= 0.45) of trace mineral supplementation on DMI, ADG, or G:F before RAC feeding. There were also no treatment effects (P >= 0.46) over all 63 d of the trial on DMI, ADG, or G: F. Despite the lack of differences in live performance, steers fed RO and RC averaged 0.10 kg/d greater (P = 0.10) carcass ADG than steers fed RZC and CONT, while steers fed RZ were intermediate and not different. Steers fed RO had the greatest (P = 0.09) carcass G: F, while steers fed CONT had the least carcass G: F, 0.0875 and 0.0774, respectively. Steers fed RO and RC averaged 5.5 kg heavier (P = 0.09) HCW than steers fed RZC and CONT, while steers fed RZ were intermediate and not different. There were no treatment effects (P >= 0.32) on LM area, 12th rib fat, marbling score, KPH, carcass yield, or USDA yield grade and distribution. However, carcasses from steers fed RC had the greatest (P = 0.10) percentage grading USDA Select. There were no treatment effects (P >= 0.20) on shear force, intramuscular fat, pH, a*, and b*. Steaks from steers fed RO and RC had 11.4% greater (P = 0.08) cook loss than steaks from steers fed CONT and RZC, whereas steaks from steers fed RZ were intermediate and not different. Also, steaks from steers fed RC had 2.11 units greater (P = 0.03) L* values (i.e., were lighter) than steaks from steers fed RZ; steaks from steers fed CONT, RO, and RZC were intermediate. In feedlot steers, the addition of both Cr and Zn supplementation did not improve growth performance or meat quality when fed in combination with 28 d of RAC supplementation; however, RAC, fed alone or in combination with Cr, did increase HCW.