Effects of ractopamine at different dietary protein levels on growth performance and carcass characteristics in finishing pigs

One hundred and twenty finishing pigs (Duroc × Landrace × Yorkshire) were allocated to four groups and used to investigate the effects of ractopamine (Rac) on growth, nutrient utilization, carcass composition and meat quality at high (180 g/kg) or low (130 g/kg) dietary protein levels. Rac, at 20 mg/kg in the diet, was fed from 64 to 90 kg live weight. In the high protein group, Rac increased ADG by 9.03% (p < 0.05) and decreased FCR by 14.48% (p < 0.05) compared to the corresponding control group, these differences were not found in the low protein groups. Pigs fed Rac had 4.5% (p < 0.05) and 4.18% (p < 0.05) higher carcass lean proportion, larger Longissimus muscle area (LMA) in both low and high protein groups, while the carcass fat proportion of Rac-treated groups were lower (p < 0.05) and fat depth were less (p < 0.05) regardless of dietary protein background. The weights of Longissimus muscle (p < 0.05), Biceps femoris (p < 0.05) and Semitendinous (p < 0.05) in Rac-treated pigs were higher than for the control groups and this for both protein levels. Furthermore, a dietary protein × Rac interaction (p < 0.05) was noted for ADG, FCR, carcass lean proportion and carcass fat proportion, but no significant effects of Rac and dietary protein on meat quality were found. These results suggest that Rac will improve the carcass characteristics regardless of dietary protein level, the favorite effect of Rac on ADG and FCR, on the contrary, will only be evidenced at a high protein level.