Forty barrows with high genetic potential for lean gain in the carcass averaging initial and final body weights of 60.43 ± 1.56 kg and 96.66 ± 3.22 kg, respectively, were used to evaluate the effect of dietary digestible lysine levels based on the ideal protein concept, on performance and carcasss characteristics. The animals were assigned to a randomized blocks design, with four treatments, five replicates and two animals per experimental unit. The treatments consisted of a basal diet formulated to contain 16.48% of CP, that was supplemented with increasing levels of HCL-L-lysine (0.70, 0.80, 0.90, and 1.00% of digestible lysine). The diets were supplemented with constant synthetic amino acids: lysine ratios based on the true digestibility. No treatment effect on feed intake was observed. It was observed quadratic treatment effects on daily weight gain and feed:gain ratio, that increased up to the estimated levels of 0.87 and 0.93% of digestible lysine, respectively, and also on plasma urea concentration, that decreased up to the estimated level of 0.83% of digestible lysine. Linear increasing treatment effect on daily lysine intake was observed, but no treatment effect on carcass length by Brazilian method, Longissimus dorsi muscle area, fat depth (10th rib), and yields of lean meat, fat, ham, and loin was observed. Carcass yield decreased as the dietary lysine levels increased. It was observed quadratic treatment effect on muscle feed:gain ratio, that increased up to the level of 0.94% of digestible lysine. The 0.94% true digestible lysine level, that corresponds to a digestible lysine intake of 26.22 g/day (2.83 g of Lys/Mcal of ME), resulted in better performance and carcass characteristics of barrows from 60 to 95 kg.
amino acids; carcass; finishing phase; genotype; urea
