Thirty six Nellore bulls, with 240 kg initial live weight (LW), were used and distributed in eight treatments, with four different concentrate levels in the diets (20; 40; 60 and 80%) and two crude protein (CP) levels (15 and 18%) with four reference bulls. After the slaughter, the carcass dressing percentage, the basic cuts percentages, the carcass length, the loin eye area, the subcutaneous fat thickness, and the carcass muscle, fat, bone, protein, ether extract, water percentages, the organs and visceral weight were evaluated. DMI in the growing phase, expressed in kg/day, was not influenced by the concentrate level, presenting mean value of 7.06. But the DMI, expressed as a percentage of the LW (% LW), in this phase, demonstrated maximum consumptions of 2.59% LW, with 42.60% of concentrate. In the fattening phase, the concentrate levels did not influence the DMI, in any of the expressed ways, with mean values of 7.16 kg/day and 1.80% LW. The increase in the diet CP level, from 15 to 18%, caused a significant increase in the growing phase DMI, but it did not influence the consumption in the fattening phase. LWG and FC were not influenced by the concentrate levels of the diet, independent of the studied phase. The diet with 18% of CP propitiated, to the bulls, 22% and 22.6% more LWG in the growing and in the fattening phases, respectively, compared to the diet with 15% of CP. In the growing phase, the diet concentrate levels did not influence the carcass dressing percentage; in the fattening phase, the increase in concentrate caused a linear increase in the carcass dressing percentage in relation to the LW. No effect was verified for concentrate level and CP level on the studied basic cuts, in both growing and fattening phases. The diet concentrate levels tended to arise fat and to diminish muscle in the carcass. In the fattening phase, the greatest CP level presented a carcass with larger muscle percentage and smaller fat percentage. In the growing phase, the kidneys, spleen, lungs, liver and the gastrintestinal tract constituents weights were not influenced by the diet concentrate and CP levels. In the fattening phase, the concentrate levels did not influence the organs and the CP level had a positive influence on the kidneys, lungs and liver weights. The rumen+reticulum, stomaches and GIT relative weights presented a linear decreasing behavior with the increasing concentrate levels. The CP level did not influence the GIT constituents weights in any of the expressed forms, in both phases.
carcass; concentrate levels; gastrointestinal tract; Nellore; protein levels; organs; roughage:concentrate ratio; Tifton hay
