Follicular dynamics during the ovulatory season in goats

Abstract

Growth and regression of ovarian follicles ≥3 mm were studied by transrectal ultrasonography for 4 interovulatory intervals in each of 5 Saanen goats. The observed number of growing identified 4-mm follicles per day differed (P<0.05) from randomness, indicating that follicles, on the average, emerged in groups (waves). Averaged over all interovulatory intervals, the number of 3-mm follicles on each day that later reached ≥6 mm followed a pattern of significant peaks on Days 0 (ovulation), 4,8 and 14. A follicular wave was defined by consecutive days of entry of follicles ≥6 mm into the wave, and the day of emergence was defined as the first day that the ≥6 mm follicles were 3 mm. In 15 of 20 (75%) interovulatory intervals, 1 wave emerged during each of Day −2 to Day 1 (Wave 1); Days 2 to 5 (Wave 2); Days 6 to 9 (Wave 3); and Days 10 to 15 (Wave 4). Ovulation occurred during Wave 4. The mean days of emergence of Waves 1 to 4 were Days −1, 4, 8 and 13, respectively. However, in 5 of these 15 interovulatory intervals, 50% of the apparent waves merged or were continuous so that a distinction could not be made between 2 waves. The largest follicle grew to a larger (P<0.05) maximum diameter for Waves 1 (8.7±0.3 mm) and 4 (9.7±0.3 mm) than for Waves 2 (7.2±0.2 mm) and 3 (7.3±0.2 mm). The following observations suggested that the phenomenon of follicular dominance was more common during Waves 1 and 4 than during Waves 2 and 3: 1) the interwave intervals (days) were longer (P<0.05) for Waves 1 (3.4±0.2) and 4 (4.3±0.6) than for Waves 2 and 3 (2.5±0.2 for each wave) and 2) the correlation between maximum diameter of largest follicle and the subsequent interwave interval was significant for Waves 1 and 4 but not for Waves 2 and 3. The 5 remaining interovulatory intervals were irregular and involved more than 4 waves, including 2 interovulatory intervals with prolonged follicular phases (14 and 21) and failures of ovulation. In conclusion, the predominant follicular-wave pattern was 4 waves with ovulation from Wave 4, and apparent follicular dominance was expressed during some follicular waves, especially during Waves 1 and 4.