Comparison of varying doses and durations of ractopamine hydrochloride on late-finishing pig carcass characteristics and meat quality

The objective was to investigate the effect of various doses and durations of ractopamine hydrochloride (RAC) on pig HCW, cutting yields, and meat quality. Late-finishing pigs (approximately 93 kg) were allotted to 12 treatments 35 d before slaughter. Treatments consisted of negative control (NEG; 13.1% CP, 0.64 TID Lys), positive control (POS; 17.8% CP, 0.94 TID Lys), and 2 RAC doses (5 and 7.4 mg/kg) with 5 different feeding durations for each dose (7, 14, 21, 28, or 35 d). Pigs on ractopamine-duration diets were fed NEG until incorporation of RAC, and then the diet was switched to POS to comply with label require- ments. A subset of 240 pigs was utilized to determine the effects of RAC on carcass cutting yields. This sub- set was selected by taking the 5 pigs closest to the aver- age pen weight from 4 complete replicates. Differences in response to RAC between 5 and 7.4 mg/kg were not significant. Therefore, RAC dosages were pooled, resulting in an average dose of 6.2 mg/kg, which was then compared with NEG and POS diets. Ractopamine increased (P < 0.05) HCW by 2.5 and 2.3 kg compared with the NEG and POS diets, respectively. Hot carcass weight also increased linearly (P = 0.003) as RAC dura- tion increased. Indicators of carcass leanness increased with RAC compared with NEG. Estimated carcass lean percentage increased (P = 0.010) 1 percentage unit from 54.79 to 55.79%, carcass cut yield increased (P < 0.001) 1.23 percentage units from 50.61 to 51.84%, and (P = 0.006) boneless lean cut yield increased 1.27 percentage units from 36.71 to 37.98%. Ractopamine decreased (P = 0.002) subjective marbling scores 0.49 units from the NEG value of 3.0, but RAC did not dif- fer (P = 0.203) from POS. Subjective color values and shear force aging curves for RAC were not significantly different from NEG or POS. Overall, RAC had greater responses in carcass weight and cut yield than NEG, and had minimal effects on meat quality.