GnRH therapy for subfertile stallions

Poor fertility has been associated with hormonal imbalances in the stallion. The primary cause of this imbalance is unknown, but it may be related to abnormal gonadotropin secretion. Secretion of GnRH from the hypothalamus causes the release of LH and FSH from the anterior pituitary and these gonadotropins help maintain adequate steroid levels so that normal spermatogenesis can occur. Hypogonadotropic hypogonadism has not been documented in the stallion; however, GnRH therapy has improved the fertility of a limited number of horses. Downregulation of the HPT axis readily occurs in most other species treated with GnRH; however, the horse seems to be unusually resistant to the development of refractoriness. Although GnRH therapy is unlikely to be beneficial to most stallions suffering from fertility problems, it is not likely to be harmful. Complete endocrine and semen evaluations should be performed on all stallions that are being considered candidates for GnRH therapy. Sequential evaluations also are necessary to monitor the stallions response to therapy. Establishment of a database containing these parameters would improve greatly our ability to diagnose and select stallions that would have the best chance of responding to GnRH therapy. Development and use of universal standards for equine gonadotropins would be the single most important advancement in equine reproductive endocrinology because as this would allow accurate and meaningful comparisons to be made between the results obtained at numerous laboratories.