Effect of constant dose and step-up ractopamine-feeding programs on live performance and carcass traits of finishing pigs in a 3-phase marketing system

The objective of this research was to determine the performance, efficiency, and carcass traits of ractopamine (RAC)- fed pigs in a step-up feeding program or a continuous dose program using a 3-phase marketing strategy. Two thousand five hundred cross-bred pigs were used in a randomized complete block design with 72 pens. Each pen initially housed 35 pigs. Twenty-six percent of the total population of pigs was sold during the first marketing period (7 d after the beginning of RAC feeding), 31% during the second marketing period (21 d after the beginning of RAC feeding), and the remaining 43% during the third marketing period (35 d after the beginning of RAC feeding). Few differences (P > 0.05) were observed in performance and carcass characteristics between the 2 RAC-feeding programs. There were no differences in starting BW ( = 83.53 kg; P = 0.54) or beginning live weight (= 95.85 kg; P = 0.32) among any of the 3 treatments groups. Pigs fed RAC had 0.17 kg/d (19.4%) greater (P < 0.0001) ADG, and had 0.07 (18.6%) greater (P < 0.0001) G:F than pigs not fed RAC throughout the 35-d feeding trial. Additionally, HCW were 3.81 kg (4.27%) heavier (P < 0.0001) and standardized fat-free lean was 1.83 kg greater (4.04%; P < 0.0001) in RAC-fed pigs than pigs not fed RAC. Both RAC-feeding strategies yielded similar improvements over control pigs when used in conjunction with a 3-phase marketing strategy.