Folliculogenesis during the transitional period and early ovulatory season in mares.

The research studies the occurrences and patterns of follicular waves in mares during the transitional period before the first ovulation of the year and the first interovulatory interval. The study discovers that there are significant differences in the growth of ovulatory follicles at the end of the transitional period and the interovulatory interval.

Research Methodology

• The researchers monitored individual follicles in 15 mares during the transitional period before the first ovulation of the year and in 9 mares during the first interovulatory interval using ultrasonography.
• They observed the growth, static phases, and regression of anovulatory follicular waves, which is identified by a dominant follicle with a diameter of 38mm or greater.
• The researchers also monitored the emergence of subsequent waves to establish the timeline and patterns of follicle growth and regression.

Findings and Observations

• During the transitional period, they discovered that seven of the mares developed one to three anovulatory follicular waves. The emergence of a subsequent wave did not occur until the dominant follicle of the previous wave was in the static phase.
• Without the emergence of waves, the researchers noticed erratic follicular activity where the follicles did not grow larger than 35mm.
• In the first interovulatory interval, 6 mares produced 2 waves (an anovulatory wave and a subsequent ovulatory wave) and 3 mares only produced the ovulatory wave.
• They observed that the ovulatory follicle at the end of the transitional period reached 20mm earlier, grew slower, but achieved a larger diameter the day before ovulation compared to the ovulatory follicle at the end of the interovulatory interval.
• The researchers also noted a longer interval from the cessation of growth of the largest subordinate follicle to the occurrence of ovulation at the end of the transitional period compared to the end of the interovulatory interval.

Conclusion

• The research concluded that there is the occurrence of rhythmic follicular waves during some transitional periods and the occurrence of two waves during some of the first oestrous cycles of the year.
• The findings offer vital insights into the occurrences and patterns of follicular development in mares which could be useful for improving breeding management and timing.