the objective of this experiment was to study the effects of different levels of supplementation on the performance, intake, digestibility, ph and rumen ammonia concentration in growing bulls grazing brachiaria decumbens stapf. pasture, during the dry-rainy transition season. for evaluation of performance, intake and digestibility, it was used 25 non-castrated steers at 11 months of age and initial average body weight of 270 kg, grouped in five plots of five animals each, following a completely randomized design. each plot received one of the following feeding treatments: mineral mixture and supplement at the proportion of 0.5, 1.0, 1.5 and 2.0 kg/animal/day, corresponding to 0.18, 0.36, 0.54 and 0.72% of the average body weight of the animals. the area designated for the animals was constituted of five 2.0-ha paddocks. for the evaluation of the ph and rumen ammonia concentration, five crossbred non-castrated steers were used, with average body weight of 240 kg, fistulated in the esophagus, rumen and abomasum, disposed in a 5 × 5 latin square, with five treatments and five experimental periods. animal performance behaved in a positive linear manner according to the supplementation levels, responding with an increase of more than 80% on weight gains of the animals. intakes of total and pasture dry matter (dm), organic matter and neutral detergent fiber were not influenced by supplementation. intakes of crude protein, non-fibrous carbohydrates, ether extract and total digestible nutrients as well as nutrient digestibility and rumen ammonia concentration showed a positive linear pattern in response to supplementation levels. increasing levels of concentrate supplementation influence positively the performance of bulls growing on pastures during the dry-rainy transition season.