This study aimed to evaluate the performance of young Nellore or dairy crossbred bulls feedlot fed silage grass with concentrate levels in the diet (600 and 900 g/kg). We used 32 young bulls, 16 Nellore and 16 dairy crossbreds, with initial average weight of 380.69 ± 10.45 and 376.94 ± 17.16 kg and, average initial age of 25 and 23 months, respectively. The experimental design was completely randomized with treatments in 2x2 factorial arrangement (two genetic groups and two levels of concentrate), using four replicates for consumption data and feed conversion and eight replicates for animal weight, weight gain and carcass characteristics. Dry matter intake (kg/day) reduced 8.8% in the concentrate, changed by the concentrate level. The apparent digestibility of dry matter and the cost of feeding increased in 19.6 e and 19.8%, respectively, The hot and cold carcass weight, subcutaneous fat thickness, conformation were not affected by concentrate level in the diet and nor by genetic group with average values of 267.32 kg; and 265.91 kg; 3.9 mm; 10.91 points, respectively. The elevation of the concentrated fraction of the diet from 600 to 900 g/kg of dry matter did not alter the amount of muscle, fat and bone of the carcass, with mean values of 64.44 e 66.52%; 19.71 e 18.72; 14.88 e 15.07%, being genetics groups 65.82 e 65.14%; 18.52 e 19.90%; 15.09 e 14.87% of cold carcass weight, respectively. The shear force necessary to cut the muscle fibers, the losses of liquid during thawing and cooking were not altered by the factors studied, with average values of 5.19 kgf/cm3, 5.79% e 23.47%, respectively.
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