Control of Ovulation - GnRH
The hormone GnRH can also be used to control ovulation. The type of GnRH used in cattle does not induce ovulation in mares. This is likely due to the a broad increase in LH that normally triggers ovulation in a mare vs. a spike in cattle. Instead, long acting agonists of GnRH have been tested for use in the mare. The first GnRH agonist tested was delivered in an implant (Ovuplant) which stimulates ovulation in 2 to 3 days. This product ceased production in the early 2000's. While effective, it was expensiven ($40.00 per implant; wholesale) and would sometimes cause a delayed return to estrus in nonpregnant mares. This was likely due to not removing all of the implant.
Although this implant is no longer commercially available, an alternative injectable form, Deslorelin, is now sold as Sucromate. A 1 ml injection to a mare with a 30 - 40 mm folicle will induce ovulation with a mean time of 42 hours and up to 90% of follicles of that size will ovulate within 48 hours.
Ferris et al., Journal of Equine Veterinary Science 32 (2012) 285-288
Artificial insemination should be 24 - 30 hours after desorelin administration with fresh semen and the same time with cooled semen. With cooled semen you can also inseminate a second time at 36 - 40 hours if ovulation has not occured but this is not required.
