Ovarian follicular dynamics in 2 to 3 months old Nelore calves (Bos taurus indicus)

This study aimed to evaluate reproductive physiology aspects in 2 to 3 months old Nelore (Bos taurus indicus) calves. Follicular dynamics was monitored daily by ultrasound in ten calves during 18 consecutive days. Calves younger than 2.25 months old (n = 4) had maximum follicle diameters <= 2.5 mm, so only the other animals (n = 6) continued to be monitored by ultrasound. The mean maximum diameter of the ovaries was 13.6 +/- 0.6 mm, which had 31.4 +/- 3.45 visible follicles. A successive anovulatory follicular wave-like pattern was identified when each wave showed a dominant follicle, including a variable number of other follicles smaller in size (subordinate follicles), during the observational period. Three consecutive follicular growth waves were detected per animal, during this time interval, when 50% of the animals (n = 3) showed two waves and the other half (n = 3) had three waves. The first day of detection of the dominant follicle, retrospectively identified at a diameter of 2 mm, was defined as the day of wave emergence on each wave (day zero). Considering the grouped data, the follicular wave length was 9.2 +/- 2.0 days and the correlated dominant follicle began its regression at 6.33 +/- 1.63 days after the day of its emergence. The dominant follicles had a growth rate of 0.23 +/- 0.06 mm/day and reached the maximum diameter of 3.03 +/- 0.17 mm. Despite the smaller ovarian and follicle diameters in 2 to 3 months old Nelore calves (Bos taurus indicus) compared to studies in post pubertal females; the follicular wave-like pattern and the number of recruited follicles were similar to the reported in Zebu females in reproductive activity. These data can characterize an early critical moment on the reproductive development of these animals.