The effect of various gonadotrophin-releasing hormone regimens on gonadotrophins, follicular growth and ovulation in deeply anoestrous mares.

This study explores the impact of different gonadotrophin-releasing hormone (GnRH) treatment plans on follicular growth, hormone release, and ovulation in mares who are in a non-reproductive state (anoestrus). The research found that the frequency and dosage of GnRH can influence ovulation.

Research Methodology

• The researchers used several regimens of the gonadotrophin-releasing hormone (GnRH) on anoestrous mares. The goal was to understand how dose and frequency affected the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), as well as the impact on ovulation and the formation of corpora lutea (structures formed after ovulation).
• The treatments included thrice daily injections of GnRH, hourly injections, and constant infusions.
• Additionally, some mares were given an implant that released a potent GnRH analogue at different rates.

Findings

• Thrice daily injections of GnRH prompted the development of pre-ovulatory follicles, but hourly injections or constant infusions were necessary to induce ovulation.
• Hourly injections stimulated a much higher LH:FSH ratio, regardless of the presence or absence of ovarian hormones.
• When anoestrous mares were given an implant that released a potent GnRH analogue at a rate of 120 micrograms/day, 55% of mares ovulated and formed corpora lutea, as compared to 77% at the 180 micrograms/day rate.
• Even at the higher dose, all mares ovulated during or within 3 weeks of the end of treatment.
• The conception rate and average day of conception matched the control group, indicating that the treatment had no negative effects on the reproductive axis.

Conclusion

• Despite pulsatile administration of GnRH being the most effective regimen for inducing an LH surge and ovulation, GnRH analogue implants are easier to administer and effectively induce ovulation.
• This suggests GnRH analogue implants can be the preferred method in many practical scenarios.