Ovarian follicular dynamics in water buffalo

Abstract

The pattern of growth and regression of ovarian follicles was characterized during 7 complete estrous cycles in 5 water buffalo by daily ultrasonographic examinations of the ovaries. Follicles ≥ 4 mm were measured and their relative locations within the ovary were determined to follow the sequential development of each individual follicle. Results indicated the presence of either one (n = 3 estrous cycles) or two (n = 4 estrous cycles) waves of follicular growth per cycle. Each wave was characterized by the development of 1 large (dominant) follicle and a variable number of smaller (nondominant) follicles. In the single follicular wave pattern, the wave started on Day 1.3 ± 0.7 (Mean ± SEM; estrus = Day 0). In the 2-wave pattern, first and the second waves started on Days 1.8 ± 0.6 and 7.8 ± 2.0, respectively, and the dominant follicle in the second wave was the ovulatory follicle. The maximal size and growth rate of the dominant follicle in the first and second wave of the 2-wave cycles did not differ significantly. However, the growth rate of the ovulatory dominant follicle in the 2-wave cycles was greater (P < 0.05) than that in the single-wave cycles. On the day of estrus, the ovulatory follicle was always the largest follicle present on either ovary. In conclusion, this study shows that in buffalo the development of ovarian follicles ≥ 4 mm occurs in 1 or 2 waves per estrous cycle.