- See also mare - hormonal analysis [Endocrine: hormone assay - female] .
- Induction of ovulation decreases the number of inseminations/mare and conserves the stallion's libido, semen quality and energy.
- Decreasing number of insemination events minimizes the chances for uterine infection in high risk mares.
- It is common for the first ovulation in the breeding season to occur at the ends of a very long estrus period with follicles persisting many days before ovulation.
- Hastening of these ovulations is frequently desirable, not always possible.
- Follicular atresia with ovulation failure may occur at any stage during the breeding season [Ovary: ovulatory failure] non-responsive to hormone treatment.
Human chorionic gonadotropin (hCG)
- hCG has LH-like activity and is obtained from the urine of pregnant women.
- It is the most efficient agent (as deslorein) for the induction of ovulation in the mare.
- hCG has no effect on an inactive ovary or one with smaller follicles (<30-35 mm in diameter). Therefore, it must be used as part of a complete fertility management program for optimal benefit.
- Doses of 1500-3000 iu → ovulation within 48 h (follicle >30-35 mm diameter).
- Can be given IV or IM.
- Higher dose rates may be required early in the breeding season and the response is more varied.
- hCG is routinely used on some studs to correlate breeding with ovulation.
- It may be used to hasten ovulation therapeutically where failure to ovulate is anticipated upon rectal examination.
- Due to the large molecular size of the protein in hCG, antibodies may be produced and anaphylaxis is a possibility.
- hCG needs to be given for 3-5 estrous cycles, however, before significant antibodies develop and antibodies have not been shown to persist until the following breeding season.
- There is no cross-reactivity with natural LH.
Luteinizing hormone (LH)
- Extracted from the pituitary glands of domestic animals.
- Less consistent results than with hCG.
Gonadotropin-releasing hormone (GnRH)
- 0.04 mg is administered intramuscularly 6 hours before mating.
- Therapy with GnRH may be indicated where serial rectal palpations suggest that a previously maturing follicle has become arrested in its development (GnRH may be more successful than hCG in the induction of ovulation in such follicles, and also in large, thick-walled follicles).
- Deslorelin is a GnRH analog available as a biocompatible short-term implant.
- Has been effective in inducing ovulation within 48 h in mares with follicles greater than 30 mm and showing characteristic signs of behavioral or physiologic estrus.
- Smaller molecular size suggests they should be less antigenic.