The objective of the experiment was to evaluate, during the growth phase, the dry matter intake, weight gain and feed to gain conversion of young bulls and steers, castrated at eight month, from two breeding systems, straightbred (Charolais - C and Nellore - N) and crossbred (¹/2 CN, ¹/2 NC), as well as to measure the resulting heterosis. The animals were confined from nine to twelve months and fed a 15% crude protein diet and a 70:30 forage to concentrate ratio. There was no difference between bulls and steers for dry matter intake (DMI) in kg/animal.day (DMID), DMI per unit of metabolic weight (DMIM) and DMI per 100 kg of live weight (DMIP). The bulls showed a 13,7% higher average daily weight gain (ADG) and were more efficient in the feed to gain conversion (4.66 vs 4.99 kg of DMI/kg of gain) than the steers. The effect of castration on the weight gain was more pronounced in calves sired by C bulls (1.00 vs 1.19 kg) than in calves sired by N bulls (.91 vs .97 kg). The F1 animals showed higher ADG than the average of the straightbreds, resulting in 9.28% heterosis. The C calves presented higher DMID and ADG than the N. However, DMIM and DMIP were similar between the two straightbred groups. The F1 ¹/2 CN and ¹/2 NC animals did not show difference for the studied variables. The calves sired by C bulls were more efficient, in the feed to gain conversion, than the calves sired by N bulls.
castration; Charolais; crossbreeding; feedlot; heterosis; Nellore
