Detailed Instructions to Mate Mares Postpartum (AAEP 2012)

If you think your job is stressful, consider the job of a broodmare--in most performance horse circles she's expected to have one foal per year for six out of seven years to be considered successful. This belief stirs up the perennial question, should you breed on the foal heat?

"There is only a period of approximately one month after foaling to establish pregnancy if the mare is to foal at the same time the following year, which is often desired," explained Tom Stout, VetMB, PhD, of Utrecht University's Department of Equine Sciences, in The Netherlands at the recent American Association of Equine Practitioners' Convention, held Dec. 1-5 in Anaheim, Calif.

Although mares come into heat within five to 12 days of foaling, and many can conceive, they might not be ready to maintain a pregnancy. The uterus might not be fully finished undergoing normal involution (returning to its regular size and shape) by the time the foal heat comes, making it uninhabitable by a fetus, or the mare could develop inflammation of the uterine lining called post-breeding endometritis.

"The major dilemma for breeders is whether to breed on the foal heat or to wait until the second heat when there is a better chance of pregnancy maintenance," noted Stout. "The catch is that not all mares will cycle normally following the foal heat."

Specific factors to consider when making this decision include:

  • Time of year the mare foals Mares that foal early in the year might be more at risk of not resuming normal estrous cycles after the foal heat (due to the decreased amount of light in the Northern hemisphere when mares' cycles are normally quiescent), but keeping such mares under lights starting two to three months before foaling can help avoid this). Late foaling, however, leaves fewer breeding opportunities, making breeding on the foal heat appealing.
  • Complications related to foaling If the mare had an infection of the placenta (placentitis), a difficult birth or dystocia, retained fetal membranes, etc., you should avoid breeding on the foal heat.
  • History of endometritis Mares with a history of endometritis might be more likely to develop this inflammation if bred on foal heat.
  • Results of a pre-breeding clinical examination Performed six to eight days post-foaling, and not to be confused with the post-foaling examination that all mares and foals should have within 24 hours of foaling, a rectal examination and ultrasound can help the veterinarian determine whether the uterus is involuting well and whether ovulation will soon occur (usually around 10-15 days post-foaling).

There are ways to manipulate the mare pharmacologically to either optimize uterine involution or delay foal heat; however, Stout recommended skipping the drugs and opting instead to perform an examination eight to nine days after foaling to assess how the mare's uterus is involuting on its own and to estimate the next ovulation date.

"If the first ovulation date is known then a mare can be treated pharmacologically to shorten the time between heats, which can save a few valuable days," advised Stout.

In other words, if the uterus is involuting well at eight to nine days after foaling and there is no evidence of any other issues, then breed on. Otherwise, try to get her to cycle normally to ensure there is no delay between the foal heat and the next regular heat. This will also allow the uterus to recover a little longer, while not pushing the mare too far off the breeding calendar for the year.

He said it's also important to optimize lighting, nutrition, and exercise to minimize these "days lost" and maximize involution.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.