Effects of Zinc, Chromium, and Beta-agonist Supplementation to Feedlot Steers on Growth Performance, Carcass Characteristics, and Meat Quality

Abstract Text: Objectives were to determine effects of supplemental Zn, Cr, and ractopamine hydrochloride (RAC) on feedlot growth performance, carcass characteristics, and meat quality. We hypothesized steers fed Zn and Cr, in combination with RAC, would have increased protein synthesis, or lean tissue accretion, and carcass quality, respectively, compared to steers fed RAC alone. Crossbred steers (n = 179; initial BW = 533 ± 94 kg) were blocked by BW and allotted to 30 pens, 10 pens per block. Pens were randomly assigned to 1 of 5 treatments: (1) control, (2) RAC, (3) Zn+RAC, (4) Cr+RAC, or (5) Zn+Cr+RAC. Steers were fed for 63 d prior to slaughter and the common basal diet contained 60% dry rolled corn, 20% corn silage, 10% distillers grains, and 10% supplement. Trace mineral (TM) treatments were included in the supplement from d 0 to 63 with targets of 1 g Zn∙hd^-1·d^-1 (KemTRACE Zn-propionate; Kemin Industries, Inc., Des Moines, IA) and 3 mg Cr·hd^-1·d^-1 (KemTRACE Cr-propionate; Kemin Industries, Inc.) for Zn and Cr treatments, respectively. From d 35 to 63, RAC (400 mg ractopamine hydrochloride as Optaflexx; Elanco Animal Health, Greenfield, IN) was top dressed immediately following feed delivery. Data were analyzed using the MIXED procedure in SAS (SAS Inst. Inc., Cary, NC). A contrast statement comparing control versus all other treatments was used to evaluate the effects of RAC. There were no treatment effects (P ≥ 0.44) on final BW, ADG, or DMI. There were also no treatment effects (P ≥ 0.32) on LM area, 12^th rib backfat thickness, marbling, KPH, USDA YG, or WBSF. However, HCW increased (trend; P = 0.06) 5 kg when steers were fed RAC, regardless of TM inclusion. Steaks from steers fed RAC, regardless of TM inclusion, had 2.0 percentage unit greater (P = 0.05) cook loss than steaks from steers fed control. Treatment affected (P = 0.03) L* values. Steers fed Cr+RAC had the greatest L* values (lightest appearing), while steers fed Zn+RAC had the lowest L* values; all other treatments were intermediate and not different from each other. These data suggest no improvement in growth performance, carcass characteristics, and meat quality when steers were fed Zn and Cr for 63 d in combination with 28 d RAC supplementation. Similar to previous reports, however, feeding RAC to steers for 28 d tended to increase HCW.

Keywords: beta-agonist, cattle, trace minerals