Development of one vs multiple ovulatory follicles and associated systemic hormone concentrations in mares.

The research article explores the development and characteristics of one versus multiple ovulatory follicles in mares, how they vary in size and systemic hormone concentrations. The study suggests that the development of multiple ovulatory follicles is associated with a greater number of follicles and higher oestradiol production at the beginning of deviation.

Follicle Induction and Classification

• The researchers induced ovulatory waves in mares through ablation of follicles measuring 6 millimeters or bigger and treatment with Prostaglandin F2 alpha (PGF2alpha) ten days post-ovulation.
• Diameter deviation was used to separate follicles into dominant and subordinate categories. This allowed the researchers to analyze and compare differences between waves with one ovulatory follicle (72% of cases) and waves with multiple ovulatory follicles (28% of cases).

Hormonal Differences in Single vs. Multiple Ovulatory Follicles

• Waves that resulted in the creation of multiple ovulatory follicles were marked by a higher count of follicles of at least 20 millimeters in size at the start of deviation.
• Such waves also exhibited different hormone concentrations. Prior to diameter deviation, these waves had significantly higher Luteinizing Hormone (LH) levels, and subsequently lower Follicle-Stimulating Hormone (FSH) concentrations on the day of deviation and thereafter. They also displayed significantly higher oestradiol concentrations two days after deviation.
• During the peri-ovulatory period (the time around ovulation), mares with multiple ovulations indicated higher oestradiol, lower FSH, higher progesterone and lower LH, starting from the day after ovulation. These varying hormone concentrations seemed to be linked to the negative impact of ovarian hormones on gonadotrophins (hormones that produce LH and FSH).

Conclusions

• The study concludes that waves linked to the formation of multiple ovulatory follicles initially contain a greater number of follicles of at least 20 millimeters in size and subsequently exhibit higher oestradiol production.
• During the peri-ovulatory period, these waves demonstrate higher oestradiol, lower FSH, higher progesterone and lower LH, starting from the day after ovulation.
• Essentially, variations in the development of one and multiple ovulating follicles were consistent with the inhibitory effects of ovarian hormones on gonadotropins.