The correlation between the number of antral follicles and ovarian reserves (preantral follicles) in purebred Bos indicus and Bos taurus cows

The objectives of this study were to compare populations of preantral follicles between purebred Bos indicus and Bos taurus cows with high or low antral follicle counts (AFC) and to correlate the number of preantral follicles with the population of antral follicles. Nelore (Bos indicus, n = 100) and Angus (Bos taurus, n = 100) cow ovaries were collected at abattoirs and examined using ultrasonography. Antral follicles ≥3 mm were counted, and the cows ovaries were assigned to high (G-High) or low (G-Low) AFC groups based on the mean number (±1 SD) of ovarian antral follicles: Bos indicus with high AFC (≥57 follicles, n = 8) or low AFC (≤21 follicles, n = 8) and Bos taurus with high (≥45 follicles, n = 10) or low AFC (≤13 follicles, n = 10). The ovaries were processed, and the number of preantral follicles was estimated. Between-groups comparisons were performed using a Kruskal-Wallis test, and the correlation between preantral and antral follicles was evaluated using a Pearson's correlation test (P ≤ 0.05). A large variation in the number of preantral follicles was observed among the animals. Although there was a correlation between the population of preantral follicles and the number of antral follicles, there was no difference between the mean number of preantral follicles in the Bos indicus G-High (48,349 ± 30,149) and G-Low groups (33,037 ± 31,710) or between the Bos taurus G-High (35,050 ± 36,060) and G-Low groups (30,481 ± 43,360). Therefore, the preantral follicle population did not differ between purebred Bos indicus and Bos taurus cattle with high or low AFC but was correlated with the number of antral follicles. In addition to the large within-groups variation in the number of preantral follicles, some cows with high AFC had lower populations of preantral follicles compared to the low AFC group, and the highest population of preantral follicles was observed in both Bos indicus and Bos taurus with low AFC.