Sexual development of Guzerat (Bos taurus indicus) bulls raised in a tropical region
Anim Reprod, vol.2, n2, p.114-121, 2005
Two-hundred and seven healthy males, 7 to 31 months of age and raised on pasture in a tropical region, were used to evaluate sexual development in the Guzerat breed (Bos taurus indicus). Body weight, body condition, testicular measurements and semen quality were recorded. Semen collection attempts were performed by electro-ejaculation at 3-months intervals, starting at 14 months of age. Thirty-eight sexually inexperienced males were used to evaluate the exhibition of sexual behavior at two age ranges: 12.1 to 17.4 months of age (G1) and 18.4 to 28.4 months (G2). Each male was evaluated individually (IND) or in groups under competition (COM); (5 males per group) free in a pasture with 5 cows (3 in heat and 2 not in heat). Body weight increased linearly from 7.5 to 30.7 months of age. Scrotal circumference and testicular diameter increased linearly with age and body weight. Testicular length had a quadratic growth with age and weight. First motile sperm cells (considered as puberty) were detected at the 18.2±2.1 months of age, 255.5±32.0 kg body weight and 24.2±2.4 cm of scrotal circumference. The percentage of bulls that exhibited sexual behavior was higher in the G2 than in the G1 group for both IND and COM evaluations. The number of sexual events displayed by active males did not differ among age groups. It was concluded that Guzerat bulls, raised in pasture under tropical conditions, reached puberty around 18 months of age, and did not reach testicular growth plateau until 30 months. Expression of sexual behavior started during the prepubertal period and differences between individuals were already detectable during this stage of development.
Zebu cattle, bulls, Guzerat, puberty, reproductive development, sexual behavior