Our objectives were to determine the effects of dose and duration of ractopamine hydrochloride (RAC) supplementation on growth performance and carcass characteristics of feedlot heifers. Heifers (n = 128) were allotted to 20 pens. Pens were randomly assigned 1 of 4 treatments: (1) 0 mg of RAC/heifer per d for 28 d, (2) 300 mg of RAC/heifer per d (Optaflexx 45; Elanco Animal Health, Greenfield, IN) for 28 d, (3) 0 mg of RAC/heifer per d for 41 d, or (4) 300 mg of RAC/heifer per d for 41 d. Heifers were fed a basal diet of 50% corn, 20% dried distillers grains with solubles, 20% corn silage, and 10% supplement (DM basis). Dry rolled corn, 0.454 kg/heifer, was removed from the diet, and 300 mg of RAC/0.454 kg of ground corn carrier was top-dressed to heifers fed RAC, daily. There were no day × RAC interactions (P ≥ 0.31) on growth performance or carcass characteristics, nor main effects (P ≥ 0.11) of duration of RAC feeding on carcass characteristics. There were no effects (P ≥ 0.22) of RAC on DMI, ADG, or G:F; however, heifers fed 300 mg of RAC had 8.4 kg heavier (P = 0.03) final BW than those not supplemented with RAC, corresponding to 9 kg greater (P < 0.01) HCW. Carcasses from heifers fed RAC had increased (P ≤ 0.03) LM area and DP compared with those from heifers not fed RAC. Feeding RAC did not affect (P ≥ 0.14) marbling, back fat, KPH, or YG. There were no interactions of RAC dose and duration; however, supplementing 300 mg of RAC/heifer per d increased final BW, HCW, LM area, and DP.
All Science Journal Classification (ASJC) codes
- Food Science
- Animal Science and Zoology