The objective of this work was to evaluate the growth of beef cattle intact or castrated at eight months, from different mating systems (MS): straightbreds (S), crossbreds of first (G1) and second (G2) generation, and of different genetic groups (GG) in each MS, S: Charolais (C) vs Nellore (N), G1: ½CN vs ½NC and G2: ¾CN vs ¾NC. Seventy-eight animals, weaned at three months, were submitted to feedlot from 7 to 12 months (first winter/spring), maintained in native pasture (NP) from 12 to 20 months (second summer/autumn), and finished in feedlot from 20 to 2 4 months (second winter/spring), when they were slaughtered. Heterosis of 20.44% for G1 and 14.44% for G2 was observed for weight at 24 months. The C was heavier than the N in all ages. In the G2, the ¾CN was heavier (P<.05) at three, eight and twelve months. Intact animals presented higher (P<.05) ADG than the castrated ones during the first feedlot period, but in NP no difference occurred between sexual condition. Heterosis for weight per day of age was 22.25% for G1 and 14.54% for G2. The G2 animals had lower ADG than the S and G1 during the first feedlot; however, in NP the response was inverse. The G2 (311g) showed higher ADG than the S (111g) and G1 (192g). Males of G1 were 75 and 22kg heavier at twenty-four months than S and G2, respectively. Also, ADG from birth to slaughter was 101 and 35g higher for G1 than for S and G2, respectively. For ADG from birth to slaugther no difference was observed between GG within mating system. However, during the first feedlot C showed higher ADG then the N (848 vs 586g), while during the summer/autumn in NP the N showed higher ADG (168 vs 55g).
Bos indicus; Bos taurus; sexual condition; heterosis; native pasture; crossbred; feedlot
