Objective was to evaluate the productive performance and carcass characteristics Nellore young bulls feedlot fed with four levels silage (100, 200, 300 and 400 g kg-1 of dry matter). Were used 32 Nellore young bulls with 383.49 ± 19 kg initial body weight, confined for 63 days and slaughtered at average weight of 482.06 kg. The experimental design was completely randomized with four treatments with eight repetitions for animal performance and carcass characteristics and four repetitions for feed consumption results. The dry matter intake was expressed in g kg-1 BW a quadratic response was obtained with maximum level consumption of 293 g kg-1 of grass silage. Inclusion silage level on diet linearity decrease apparent digestibility of dry matter. Silage proportions was not changed weight gain. Diet grass silage level not affected hot and cold carcass weights, fat thickness, conformation and physiological maturity, showing mean values of 271.30 kg; 270.19 kg; 3.81 mm; 10.78 and 12.84 points, respectively. Among the primary cuts carcass (cold carcass % weight) only rib proportion was modified by diet, increasing linearly with the advance of the forage level in diet. Among the secondary commercial cuts of the carcass, topside weight changed by diet, with larger weight for diet containing 300 g kg-1 of grass silage/kg diet dry matter. The increase proportion of the silage diet from 100 to 400 g kg-1dry matter did not alter muscle, fat and bone carcass amount with average values of 64.75; 19.77 and 15.62% of the cold carcass weight, respectively. The muscle fibers shear force, thawing and cooking liquid loss were not changed by grass silage diet levels, with mean values of 5.78 kgf/cm3, 6.16% and 25.54%, respectively. The inclusion of grass silage up to 400 g kg-1 of dry matter diet does not change body development of feedlot young bulls, providing carcass and meat production with suitable marketing quality.
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