This study was carried out with 38 young bulls, with initial ages between 426 and 462 days, and final ages between 745 to 781 days, and from several breeds (Nelore, Guzerá, Gir and Caracu). They were divided into seven genetic groups. It was compared reproductive development considering the morphological and physical characteristics of the ejaculate (volume, aspect, motility and strenght, morphology and concentration of spermatozoa) collected at 29-day-interval (stage). The bulls from Selection Nelore (NeS, n=6), Traditional Nelore (NeT, n=9) and Selection Caracu (CaS, n=6), (415, 430 and 419kg of weight, respectively) groups showed significant differences in all characteristics when compared to Control Nelore (NeC, n=4) group at the second stage, which was also the only group with significant difference in relation to the other six groups on the eleventh stage (P<0.05). Significant differences in the average of progressive motility of the spermatozoa were registered in the third stage between groups CaS (68.3%) and Traditional Guzera (GuT, n=5) (10.0%) as well as between CaS (76.7%) and NeS (45.0%) on the fourth stage (P<0.05). Differences in the total defects of the spermatozoa were not found on the second and eleventh stages. Based on the morphology of the spermatozoa, it is concluded that the young bulls from genetic groups NeT, CaS, Selection Gir (GiS, n=4), Selection Guzera (GuS, n=4), NeC, GuT and NeS reached sexual maturity at 547, 532, 578, 544, 547, 572 and 600 days of age and body weight of 430, 440, 389, 420, 336, 451 and 438kg, respectively.
Bovine; semen; morphology; sexual maturity
