The effects of ractopamine hydrochloride feeding programs on growth and carcasses of finishing pigs marketed in 2 different groups

The objective was to evaluate pig performance, feed efficiency, and carcass characteristics of finishing pigs fed ractopamine hydrochloride (RAC) in a single-phase (7.4 mg/kg for 31 d) or step-up (5.0/10 mg/kg) feeding program when compared with a NRC control diet. Barrows and gilts were divided into pens of approximately 22 pigs per pen and fed one of 3 dietary programs when pigs reached approximately 103.5 kg of BW. The 5 heaviest pigs per pen were marketed on d 17 of the trial (before the step-up initiation), and on d 31 the remaining 17 pigs per pen were marketed. Pigs fed RAC and marketed after 17 d (1.195 kg/d) of feeding had a 14.5% improvement (P < 0.0001) in ADG and a 13.2% improvement (P < 0.0001) in efficiency (0.385) compared with controls (1.04 kg/d; 0.34). On average, RAC-fed pigs had 0.43 percentage units greater (P = 0.02) carcass yield. During the entire 31-d feeding trial, RAC-fed pigs (1.20 kg/d) gained 12% more (P < 0.0001) weight per day and were 14% more (P < 0.0001) efficient (0.365) at feed conversion than were controls (1.07 kg/d; 0.32). Ractopamine-fed pigs also had greater (P < 0.0001) carcass yields, larger (P < 0.0001) loin depths, and greater (P < 0.0001) estimated carcass lean values than did pigs not fed RAC. Ractopamine can be fed in a step-up feeding program even in marketing strategies when pigs are marketed relatively soon after the RAC initiation with the same performance and carcass results normally observed in continuous-dose feeding programs.