Hormonal mechanism of follicle deviation as indicated by major versus minor follicular waves during the transition into the anovulatory season in mares.

The research investigates the hormonal mechanisms that influence follicle growth in mares during the transition into the anovulatory season. The investigation was aimed at comparing follicle growth and hormone concentrations between an interovulatory interval and the initial 60 days of the anovulatory season.

Research Methodology

• The research was conducted on pony mares starting from November. The mares were divided into three groups for observations.
• The first group had ovulatory mares where follicles of ≥6 mm in diameter were ablated at day 10 following an ovulation that initiated an interovulatory interval.
• The second and third group had anovulatory mares where follicles of the same size were ablated at day 10 and day 60 after the last ovulation of the year, respectively.

Defining Follicular Waves

• The follicular waves were categorized into major and minor waves depending on the presence or absence of a dominant follicle respectively.

Research Findings

• Post-ablation data showed that 100% of ovulatory mares exhibited major waves whereas only 33% and none of the anovulatory-10 and anovulatory-60 group mares showed major waves respectively.
• Conversely, minor waves were observed in 0, 67, and 100% of ovulatory, anovulatory-10, and anovulatory-60 groups respectively.
• Minor waves were detected in 83% of anovulatory mares between day 20 and day 60.
• The growth of the largest follicle was similar for both major and minor waves until the deviation’s onset in the major waves.
• FSH surges after ablation were observed to be similar for all groups as well as for surges detected between days 20-60.
• LH concentrations were higher in association with major waves than with minor waves.
• Both the diameter of the largest follicle and LH concentrations for minor waves were greater after ablation at day 10 after the last ovulation of the year than after ablation at day 60.

Conclusion

• The results indicated that some mares developed major follicular waves early in the anovulatory season and that minor waves developed throughout the first two months.
• Despite similar FSH surge that stimulate wave growth, differences in follicle growth were noted and were attributed to differences in LH concentrations on a temporal basis.
• A minor wave developed into a major wave when the largest follicle reached a diameter characteristic of the deviation’s start in the presence of an adequate LH stimulus for the growth of a dominant follicle.