Meta-analysis of the relationship between ractopamine and dietary lysine levels on carcass characteristics in pigs

A meta-analysis was carried out to evaluate the relationship between ractopamine and dietary lysine levels on carcass characteristics in pigs. The database was composed by 29 articles published in international journals from 1990 to 2007, totalizing 155 treatments and 3786 pigs. Average inclusion of ractopamine was 15.3 ppm (ranging from 0 to 30 ppm) and daily average intake of ractopamine was 24.9 mg. Ractopamine addition increased (P < 0.05) hot carcass weight in 4%, loin area in 12% and lean meat content in 4%. Pigs supplemented with ractopamine presented decrease (P < 0.05) of 8% in backfat thickness at the tenth rib, 3% in backfat thickness at the last rib and 5% in mean backfat thickness. Each increase in 1 mg of ractopamine intake represented a reduction of 0.3 mm in tenth-rib (Y = 29.61–0.308 RAC + 0.025 RAC2, R2 = 0.81, RAC: ractopamine intake expressed in mg) and 0.5 mm at last-rib backfat thickness (Y = 30.52 + 0.519 RAC–0.0054 RAC2, R2 = 0.94). The use of ractopamine affected (P > 0.05) neither carcass length and dressing, nor meat marbling and color. Loin area was positively correlated (r = 0.27, P < 0.05) and mean backfat thickness was negatively correlated (r = − 0.27, P < 0.05) to dietary lysine concentration. Pigs supplemented with ractopamine whose daily intake of lysine per unit of metabolic weight was more than 195 mg presented (P < 0.05) loin area 4% higher and backfat thickness 10% lower than other animals. Supplemented pigs that received diets with lysine content superior to their calculated amino acid requirement presented weight gain 14% higher, lean meat content 17% higher, leaf fat 34% lower and loin area 6% higher when compared to other supplemented animals. Ractopamine increases lean meat content and reduces backfat thickness in carcass, however, the interaction between additive and nutritional components must be considered in diet formulation.