Effect of feeding ractopamine hydrochloride (Optaflexx) with or without supplemental zinc and chromium propionate on growth performance, carcass characteristics, and meat quality of finishing steers.

Abstract

Objectives of this study were to determine the effects of feeding ractopamine hydrochloride (Optaflexx) with or without supplemental Zn propionate (KemTRACE Zn) and Cr propionate (KemTRACE Cr) to finishing steers on growth performance, carcass characteristics, and meat quality. Angus cross steers (n = 142; BW = 527 ± 14 kg) were blocked by BW into 4 blocks (6 pens/block, 5 to 6 steers/pen). Steers targeted at an average 12th rib back fat thickness of 1.3 cm via ultrasound, by block, were randomly assigned to 1 of 3 dietary supplements for the final 35 d of feeding before slaughter: 1) no supplementation, where analyzed Zn and Cr were 49.82 and 0.98 mg/kg (DM basis), respectively (CONT), 2) 300 mg ractopamine hydrochloride·steer(-1) · d(-1), where analyzed Zn and Cr were 49.38 and 0.96 mg/kg (DM basis), respectively (RAC), or 3) 300 mg ractopamine hydrochloride, 1.0 g of Zn supplied as Zn propionate (KemTRACE Zn), and 3 mg of Cr supplied as Cr propionate (KemTRACE Cr) steer(-1) · d(-1), where analyzed Zn and Cr were 159.73 and 1.25 mg/kg (DM basis), respectively (RAC+TM). All steers were fed the same basal diet of 20% corn silage, 20% dried distillers grains, 50% corn, and 10% mineral-vitamin supplement (DM basis). Data were analyzed as a randomized complete block design with a fixed effect of treatment and a random effect of block. Average daily gain and G:F were increased (P < 0.01) by 16% in steers fed RAC when compared with steers fed CONT. However, ADG and G:F were not different (P ≥ 0.61) between steers fed RAC and RAC+TM. Furthermore, HCW was increased (P = 0.04) by 1.87% (6.61 kg) in steers fed RAC when compared with steers fed CONT, whereas HCW was not different (P = 0.80) between steers fed RAC and RAC+TM. Back fat thickness and marbling were not different (P ≥ 0.14) between steers fed RAC and CONT or (P ≥ 0.34) between steers fed RAC and RAC+TM. Warner-Bratzler shear force tended to be greater (less tender; P = 0.06) in steers fed RAC when compared with steers fed CONT yet was not different (P = 0.34) between steers fed RAC and RAC+TM. However, meat quality, as measured by pH, objective color, and moisture composition, did not differ (P ≥ 0.55) between steers fed RAC and CONT. Although steers fed RAC had improved ADG, feed efficiency, and HCW in this study, feedlot growth performance and carcass characteristics were not further improved by additional supplemental Zn and Cr.