Efeito da ractopamina e de métodos de formula？？o de dietas sobre o desempenho e as características de carca？a de suínos machos castrados em termina？？o

an experiment was conduced with the objective of evaluating the effects of diet formulation methods and supplementation of ractopamine (rac) on the performance and carcass characteristics of finishing barrows. sixty commercial hybrid swines were used, distributed in a randomized experimental block design, in a 2 x 3 factorial arrangment, with two levels of rac and three methods of diet formulation. supplementation with rac improved the final weight, daily weight gain (dwg) and feed conversion (fc) of the finishing barrows. addition of rac improved also the carcass characteristics by reducing the backfat thickness in point p1 and increase daily lean meat deposition rate. diets formulated based in the concept of ideal protein or by the increase of soybean meal provided better results on fc, but did not influence significantly daily feed intake, dwg and carcass characteristics. finishing barrows supplemented with rac during 21 or 28 days showed better performance and carcass quality. diets formulated to attend the levels of digestible lysine by the inclusion of l-lysine hcl with the adjustment of other amino acids for ideal protein relation (ideal protein) or by the greater inclusion of soybean meal (increase of cp) provided better results of feed conversion in finishing borrows supplemented with rac during 28 days.