by Dr. Frederick Harper
UT Animal Science Department

Posted December 26, 2001

After weeks of winter weather, we think that spring has arrived when we get one day of sunshine.

But the mild days in late winter can be frustrating for broodmare owners who have open or barren mares. One of the most common questions is, “What’s wrong with my mare?”

Well, the answer is rather simple, even though the broodmare owner doesn’t like it. Nature takes its time. Several factors are at play.

Human intervention really messed up the horse-mating industry. Years ago in England, it was decided that all registered horses would have a common birthday of Jan. 1. No matter when a foal is born this year, it’ll be a year old on Jan. 1, 2002. But owners want their mares to foal early in the year based on the idea that bigger is better and early foals are bigger.

Herein lies the major problem. Nature doesn’t work on this timetable. Mares don’t mate until the days get longer in the spring. Length of daylight, as well as nutrition and warmer weather are key factors in nature’s process.

In the winter most mares become anestrus. In other words they don’t have estrous (mating) cycles like those that occur in spring, summer and early fall. Spring is a transition period during which the mare’s reproductive system must gear up for mating and pregnancy.

In the spring transition the mare’s reproductive system is unpredictable, giving owners ulcers and sleepless nights. Some mares in spring transition exhibit behavioral estrus (heat), which may last only a day or maybe for several weeks. During spring transition mares don’t ovulate. Mares cannot become pregnant until they ovulate, which normally doesn’t occur until about April 7. Mating the mare before this time is a waste of time and money.

What’s an owner to do?
Artificial lights can fool the mare into thinking it’s spring. But to be effective you have to put them under lighting at least by Dec. 1.

Hormone programs may aid in shortening the transition period. But only your veterinarian or a reproductive equine specialist should administer such programs.

Most mare owners probably just need to cool their heels and wait on nature to get “Old Molly” cycling regularly.

This isn’t a bad plan. Most foals are born in April and May anyway. Nature planned births when pastures are green and the weather milder. Management of foaling mares and newborn foals is easier and less risky at this time of year too.

Owners planning to use shipped cool or frozen semen need to put these orders on hold until their mare(s) are reproductively functional. Mares that you’ll transport to the stallion can stay home in a known environment until ready for romance.

Use the next 60 days to make sure that mares are healthy and in moderate body condition in preparation for nature’s intended mating season. Where practical use ultrasound or palpation to determine when the mare will ovulate. Mares usually have three to four large follicles (larger than 30 mm) before their first ovulation.