Recombinant Hormones Make Mares Cycle in Winter (AAEP 2011)

Researchers reported success with inducing ovulation in winter anestrous mares via a new hormone therapy.

No account yet? Register


People have successfully shortened or lengthened mares’ estrous cycles for decades, but it’s a much taller order to induce cycling in a mare that’s not cycling at all. However, researchers recently reported good success with inducing ovulation in winter anestrous (noncycling) mares via a new hormone therapy regimen at the 2011 American Association of Equine Practitioners convention held Nov. 18-22 in San Antonio, Texas.

Veterinarians and owners have traditionally used artificial lights  to  stimulate mares to ovulate earlier in year (February) instead of waiting until the onset of the natural or physiologic breeding season (April). People have also successfully shortened or  lengthened estrous cycles to synchronize donor and recipient mares for oocyte or embryo transfer.

Researchers at Colorado State University, the University of Kentucky, and the University of California, Davis, have taken this process one step further by using recombinant equine follicle-stimulating hormone (reFSH) to induce follicle development and subsequent ovulation in deep anestrus mares (the stage they’re generally in midwinter).

The hormone eFSH has been used in the past to stimulate donor mares’ ovaries to increase the number of ovulations (i.e., superovulation) and thereby increase the number of embryos that may be recovered during  one cycle

Create a free account with to view this content. is home to thousands of free articles about horse health care. In order to access some of our exclusive free content, you must be signed into

Start your free account today!

Already have an account?
and continue reading.


Written by:

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

Related Articles

Stay on top of the most recent Horse Health news with

FREE weekly newsletters from

Sponsored Content

Weekly Poll

sponsored by:

Which skin issue do you battle most frequently with your horse?
238 votes · 238 answers

Readers’ Most Popular

Sign In

Don’t have an account? Register for a FREE account here.

Need to update your account?

You need to be logged in to fill out this form

Create a free account with!