With the increasing dependence on reproductive techniques that require well timed ovulation, there has been a steady push for systems and drugs to control cycling and the time of ovulation. Artificial insemination, embryo transfer, and minimal contamination techniques for subfertile mares are all examples of techniques that benefit from a predictable time of ovulation. Even for natural service of healthy mares, a well timed ovulation will decrease the number of covers allowing for more mares to be bred to a stallion.

The hormone that naturally causes maturation and ovulation of the follicle is luteinizing hormone (LH). It is released from the pituitary gland in response to increasing levels of gonadotropin releasing hormone (GRH) where it circulates to the growing follicle and stimulating maturation and ovulation. Currently there are two commercial products available that hasten ovulation of a maturing follicle:

• Human chorionic gonadotrophin (HCG) which has LH properties. There are many commercial HCG products available.
• Deslorelin has GRH properties which stimulate natural LH. Deslorelin is manufactured by Fort Dodge and marketed under the name Ovuplant...more.

This article discusses HCG in reproduction, cyrptorchids, its use, pharmokinetics, side effects, drugs interactions, and dosage. The specific use of these drugs in equine reproduction and their properties are discussed and contrasted in Equine Reproduction » Breeding and Foaling » Heat (Estrus) Detection, Ovulation Prediction, and Timing Insemination.

In mares HCG has similar effects to luteinizing hormone (LH) and can induce ovulation in a maturing follicle. In stallions it will stimulate the release of testosterone.