A total of 2,158 crossbred pigs was used to evaluate the effects of feeding 7.4 mg/kg ractopamine hydrochloride (RAC) on the growth performance and carcass characteristics of heavy-weight finishing pigs sent to slaughter using a 3-phase marketing strategy. The study was performed from 121.0 ± 4.28 kg to 144.5 ± 4.73 BW using a randomized complete block design (blocking factor was d of start on test) with 2 treatments (0 vs. 7.4 mg/kg RAC). Pigs were housed in a commercial wean-to-finish facility in groups of approximately 25 (44 groups/treatment), with ad libitum access to feed and water throughout the study, and pen weights of pigs were recorded at the start (d 0), and on d 7, 21, and 35 of study. Pigs were sent for slaughter according to the following marketing strategy: 1) after 7 d on RAC, the heaviest 16% of each pen was sent for slaughter (Phase 1), 2) after 21 d on RAC, the next 40% of each pen was sent for slaughter (Phase 2), and 3) after 35 d on RAC, the remaining 44% of each pen was sent for slaughter (Phase 3). Pigs were selected for slaughter by visual appraisal and shipped to a commercial facility where standard carcass measurements (HCW, LM depth, and backfat depth) were measured. Overall, feeding RAC increased (P < 0.001) ADG (18.8%) and G:F (23.7%) compared to the control, but lowered (P < 0.001) ADFI (3.3%). In addition, feeding RAC increased (P < 0.001) HCW (3.9 kg), carcass yield (0.7% units), LM depth (5.0%), and predicted lean content (1.0% units), and reduced backfat depth (6.3% lower) compared to controls. With each subsequent phase of marketing, the magnitude of improvements in response to feeding RAC decreased for ADG (43.1, 20.9, and -3.1% for Phase 1, 2, and 3, respectively) and G:F (37.5, 25.8, and 6.4% for Phase 1, 2, and 3, respectively); however, improvements in HCW (1.6, 4.5, and 4.2 kg for Phase 1, 2, and 3, respectively), carcass yield (0.2, 0.6, and 0.9% units for Phase 1, 2, and 3, respectively), LM depth (2.3, 5.7, and 5.2% for Phase 1, 2, and 3, respectively), and predicted lean content (0.2, 1.0, and 1.3% units for Phase 1, 2, and 3, respectively) generally increased from feeding RAC. These results suggest that while improvements in growth performance from feeding RAC will generally decline after 21 d of feeding, improvements in carcass traits, particularly carcass yield and lean content, will continue with feeding RAC until d 35.
Keywords: Paylean; carcass; growth; marketing; pigs; ractopamine.