Induction of ovulation in anoestrous mares with a slow-release implant of a GnRH analogue (ICI 118 630).

The research involves inducing ovulation in mares in a state of anoestrus, using a slow-release implant that contains a Gonadotropin-releasing hormone (GnRH) analogue. The results suggest that this method can efficiently trigger ovulation, leading to successful conception in a significant number of the mares.

Study Design and Methodology

• This study included 18 experimental pony and 136 commercial Thoroughbred mares, all of which were either in a state of seasonal or lactation-related anoestrus (lack of normal reproductive cycle).
• The mares were injected subcutaneously with one or two slow-release implants. The implants were made of a D,L-lactide-glycolide co-polymer and were impregnated with 0.9 or 1.8 mg of a powerful GnRH analogue, ICI 118 630.
• The implants were designed to release 30 or 60 micrograms of the GnRH analogue each day for 28 days.
• A subset of 32 Thoroughbred mares was also given a daily oral dose of 27.5 mg allyl trenbolone for 5 days following the implant injection.

Results and Observations

• Out of the total mares treated, 76% of the pony mares and 88% of the Thoroughbred mares ovulated between 3-18 days after the treatment.
• The additional treatment of allyl trenbolone didn’t noticeably decrease the variation in time between treatment and ovulation.
• Around 70% of the mares that were mated during the oestrus phase induced by the GnRH analogue successfully conceived.

Conclusion

• The trial demonstrated that using slow-release implants of low-dose GnRH analogues can be an effective and practical way to hasten renewed ovarian cyclicity in mares that are in a state of anoestrus.
• This research presents a potential practical solution for reinitiating the reproductive cycle in mares that are not in breeding season or those that have paused their cycle due to the demands of lactation.