Management for Early Breeding - GnRH
GnRH has been used to hasten breeding season in mares. It works by stimulating the release of FSH and LH. Follicles begin to grow produce estrogen and then the estrous cycle will in theory continue. Increasing prolactin secretion also appears effective. You have several choices if you attempt to use GnRH, eFSH or prolactin increase to induce an early estrus and ovulation:
- Deslorelin (GnRH agonist; 50 µg, subcutaneous, 2 times/day
until ovulation)
- In 2010, Deslorelin was approved for induction of ovulation in mares and is marketed as Sucromate at 1.5 mg/ml of Deslorelin. Veterinarians may no longer import Deslorelin from other sources. Note that 50 µg of Deslorelin is 33 µl of the Sucromate product. This is not a measurable amount. Therefore although possible, Deslorelin is no longer possible to use for hastening the breeding season.
- Buserelin (GnRH agonist10 µg, SC), every 12 hr plus hCG (2,500 IU, IV) once a follicle has reached 35 mm in diameter. This is not FDA approved but still possible for use in 2014.
- eFSH : 2 times/day for 5 days; ovulation in 7.6 days (cost was $300/mare but no longer available in US)
- Osmotic minipumps (deliver GnRH in pulses)
- Domperidone (dopamine receptor antagonist; Equidone; 1.1 mg/kg/day, by mouth) has also been used to stimulate follicular development in mares with quiescent ovaries.
Deslorelin is currently (2014) sold as Sucromate, induces ovulation of >30 mm follicles but use for development of smaller follicles no longer practicle. Other GnRH agonist such as Buserelin are still possible for growth of follicles. The use of eFSH is no longer possible in US. Domperidone works on mares that are first treated with 16 hrs light for 2 weeks and then given Domperidone for 3 weeks or until ovulation. All of the methods shown above are costly and involve lots of work. In addition they are only effective when the mare is in the late transition period. These methods are most often used for problem mares that have not begun to cycle normally by April.
