145
Effects of dose and duration of ractopamine hydrochloride supplementation on growth performance and carcass characteristics of feedlot heifers
Previous work has shown that ractopamine hydrochloride improves live BW gains, G:F, and HCW; however, data are lacking regarding duration of feeding 300 mg to heifers on growth performance and carcass characteristics. Objectives of this study were to determine the effects of dose, 0 or 300 mg/hd d-1, and duration, 28 or 41 d, of ractopamine hydrochloride (RAC, Optaflexx, Elanco Animal Health, Greenfield, IN) supplementation on growth performance and carcass characteristics of feedlot heifers. Charolais cross heifers (n = 128) were blocked by BW into 2 blocks and allotted to 20 pens. Pens were randomly assigned 1 of 4 treatments in a 2x2 factorial arrangement: (1) 0 mg RAC/hd d-1 for 28 d, (2) 0 mg RAC/hd d-1 for 41 d, (3) 300 mg RAC/hd d-1 for 28 d, or (4) 300 mg RAC/hd d-1 for 41 d. Heifers were fed a basal diet of 50% dry rolled corn, 20% DDGS, 20% corn silage, and 10% supplement. Ractopamine hydrochloride was top dressed immediately following feed delivery. Cracked corn was removed from the diet and 300 mg RAC per 0.454 kg of ground corn carrier was top dressed. Data were analyzed using the mixed procedures in SAS. There were no day×RAC interactions (P ≥ 0.30) for heifer growth performance. There was no effect (P ≥ 0.16) of RAC on DMI, ADG, or G:F; however, feeding 300 mg RAC tended to increase (P = 0.08) final BW by 16.3 kg, regardless of duration fed. Heifers fed RAC for the last 28 d before slaughter tended to have greater (P = 0.09) G:F, but there was no effect (P > 0.15) of duration on any other performance measures. There were no day×RAC interactions (P ≥ 0.36) for heifer carcass characteristics. Furthermore, there were no effects (P ≥ 0.20) of duration of RAC feeding on heifer carcass characteristics. However, heifers fed RAC had an average increase (P = 0.03) of 12.9 kg of HCW, regardless of duration fed. Heifers fed RAC also had greater (P ≤ 0.05) LM area and dressing percentage. There was no effect (P ≥ 0.12) of RAC on marbling, 12th rib fat, KPH, or YG. Therefore, supplementing RAC at 300 mg/hd d-1to heifers increased HCW, LM area, and dressing percentage and tended to increase final BW without affecting other measures of performance.
Keywords: beef, carcass, heifers, ractopamine