Comparison of Antral and Preantral Ovarian Follicle Populations Between B os indicus and B os indicus‐taurus Cows with High or Low Antral Follicles Counts

Contents The objective was to compare populations of antral and pre‐antral ovarian follicles in B os indicus and B os indicus ‐ taurus cows with high and low antral follicle counts. Nelore ( B os indicus, n = 20) and Nelore X Angus (1/2 B os indicus‐taurus, n = 20) cows were subjected to follicular aspiration without regard to the stage of their oestrous cycle (day of aspiration =  D 0) to remove all follicles ≥3 mm and induce growth of a new follicular wave. Ovaries were examined by ultrasonography on D 4, D 19, D 34, D 49 and D 64, and antral follicles ≥3 mm were counted. Thereafter, cows were assigned to one of two groups: high or low antral follicular count ( AFC , ≥30 and ≤15 antral follicles, respectively). After D 64, ovaries were collected after slaughter and processed for histological evaluation. There was high repeatability in the numbers of antral follicles for all groups (range 0.77–0.96). The mean (± SD ) numbers of antral follicles were 35 ± 9 ( B os indicus ) and 38 ± 6 ( B os indicus ‐ taurus) for the high AFC group and 10 ± 3 ( B os indicus ) and 12 ± 2 ( B os indicus‐taurus ) follicles for the low AFC . The mean number of preantral follicles in the ovaries of B os indicus ‐ taurus cows with high AFC (116 226 ± 83 156 follicles) was greater (p < 0.05) than that of B os indicus cows (63 032 ± 58 705 follicles) with high AFC . However, there was no significant correlation between numbers of antral and preantral follicles.