The effects of dietary ractopamine on the performance and carcass characteristics of late-finishing market pigs with a previous history of porcine circovirus type 2 associated disease (PCVAD)

Porcine circovirus type 2 associated disease (PCVAD) is a costly disease to the commercial pig industry. Clinically significant PCVAD decreases growth rate and increases mortality in growing pigs. Porcine circovirus type 2 can costs the US swine industry 3 to 4 dollars per pig and in extreme cases as much as $20 per pig because of increased mortality rates and reduced growth performance of infected pigs relative to pigs of higher health. A total of 1,635 barrows and gilts with a known history of PCVAD were used in a randomized complete block design with a 5 × 2 factorial arrangement of the following treatments: no ractopamine hydrochloride (RAC), 5.0 mg/kg of RAC for 21 d, 7.4 mg/kg of RAC for 21 d, 5.0/7.4 mg/kg step-up, or 5.0/10.0 mg/kg step-up feeding program in barrows and gilts. Pigs assigned to the step-up program were fed the initial dose of 5 mg/kg of RAC for the first 14 d of the trial and then stepped-up to the increased dose of 7.4 or 10.0 mg/kg for the final 7 d of the feeding period. Growth performance traits were measured weekly during the 21-d test period, and carcass traits were measured on d 21 at the slaughter facility. Growth advantages of RAC-fed pigs over controls were observed as early as 7 d on trial and persisted throughout the entire live phase of the experiment. Pigs fed RAC gained 18.6% more weight per day than did control-fed pigs (1.02 vs. 0.86 kg/d, P < 0.0001) during the feeding period and were almost 21% more (P < 0.0001) efficient (G:F) than were control-fed pigs. Loin depths of RAC-fed pigs were 0.31 cm greater (P < 0.0001) and estimated carcass lean percentages were 0.62 percentage units greater (P < 0.0001) than those of controls. Collectively, these data suggest that RAC supplementation is an effective means of improving growth performance and carcass composition in finishing pigs with a clinical history of PCVAD early in the grow-finish period.