Forty Nellore bulls, with 240 kg initial live weight (LW), were used. Four were reference bulls, four were fed for maintenance, and the remaining were allotted to eight treatments, with four different concentrate levels in the diets (20, 40, 60, and 80%) and two levels of crude protein (CP) (15 and 18%). The growing phase was evaluated up to 360 kg of LW and the fattening phase, up to 450 kg of LW. Cynodon dactylon (L) Pears. (cv Tyfton 85) grass hay was used as roughage. After slaughter, all animal body parts were weighed and sampled. The samples were freeze dried to determine the dry matter, pre-degreased with ether, grinded and the concentrations of macrominerals were determined. The Ca, P, Na and Mg contents in the body were determined in function of their concentrations in the several body parts. The macrominerals contents retained in the body were determined by regression equations of the logarithm of the macrominerals contents in the body, in function of the logarithm of empty body weight (EBW). By deriving the prediction equations of macrominerals body content, in function of the logarithm of empty body weight (EBW), the net macrominerals requirements, for gains of 1 kg of EBW, were obtained by means of the equation Y' = b. 10ª. Xb-1, being "a" and "b" the intercept and the regression coefficient, respectively, of the prediction equations of macrominerals body contents in the body. There was a decrease in the empty body and in the gain of empty body concentrations of the five macrominerals studied, with the increase of the live weight. The g Ca/100 g relations of retained protein and g P/100 g of retained protein were 6.44 and 4.78, respectively.
macrominerals; Nellore; requirements
