The objective of this study was to evaluate performance and nutritional traits of beef cattle raised on pastures, castrated at different ages, with and without supplementation. Forty-four crossbred young bulls with predominance of Zebu breed at initial average age of 120±30 days were used in the experiment. Animals were distributed in a completely randomized design in a factorial arrangement with four ages of castration and two supplementation systems. The animals were distributed into four groups and placed on Brachiaria decumbens Stapf pastures, where they were fed concentrate supplementation or mineral salt ad libtum (control). Animals were castrated at 120, 240 and 360 days of age with average body weight of 115, 175 and 276 kg, castrated or not, in each supplementation group. Concentrate supplement composition and the amount supplied to the animals varied according to the time of the year and development phase of the animals. Trials were carried out to evaluate nutritional variables in each of the following phases: suckling, growth in the dry season and growth in the dry/rainy transition season. Concentrate supplementation improved the use of pasture, although it may have caused substitutive effect in all seasons evaluated. Castration of the animals before the dry season impaired animal development until the following dry/rainy transition season, especially when carried out during weaning. Concentrate supply may reduce some effects of this stress.

The objective of this experiment was to estimate the requirements of energy, protein and macrominerals of grazing crossbreds calves, in Brachiaria decumbens Stapf pasture, castrated at different ages, with and without supplementation. Forty-seven young calves at initial age of 120±30.1 days and 115.3±1.97 kg of live weight were used. To estimate net energy requirements for weight gain, a regression equation between energy retained in the gain and empty body weight gain and metabolic empty body weight was obtained. For estimation of net protein requirements for weight gain, a regression equation was adjusted between protein retained in gain and empty body weight gain and energy content of this gain. Net requirements of Ca, P, Mg and Na for weight gain were determined by the equation Y' = a.b. Xb-1, in which a and b represent the intercept and the coefficient of the alometric equation of macromineral body content prediction, respectively. Neither castration nor concentrate supplementation affects body weight gain net requirements, except the ones of Ca, which were higher for non-castrated animals.