Preparing Your Mare for Breeding Season

Not having your mare in optimal condition to conceive when you are ready to breed her results in lower fertility, frustration, and financial losses that can extend through this season and into the next. The critical things to check for are: is she having regular heat cycles, does she have a uterine infection, and is she in good body condition?

Her maintenance healthcare including vaccinations, deworming and preventative dental work should also be reviewed and updated several weeks before going to stud.

To ensure she is having regular cycles and ovulating the mare needs to be exposed to increasing day length starting 2 to 2.5 months before you want to breed her. For example, for mare owners wanting to breed in February, the supplemental lighting program should have been started right after Thanksgiving or early in December. Even if you want a March or April foal, it is a good idea to start mares under lights as early as January, as it isn’t unusual for mares that have not received light treatments to not cycle naturally until the early part of May.

The old standby of 16 hours of continuous light a day is easy and highly effective. The supplemental light is added in the evening, and in winter, this generally means the lights need to be on until 11 pm.

The rule of thumb for supplemental light intensity is being able to read a newspaper comfortably anywhere in the stall, which translates to a 200-watt incandescent bulb or two 40-watt fluorescent tubes. Pregnant mares that are due to foal early in the season should also be put under lights as it isn’t unusual for them to stop cycling for a while after their foal heat.

Many stud farms require a uterine culture (prebreeding swab) on open mares before they will accept them for breeding to rule out infection. This can also benefit the mare owner as an undiagnosed infection can waste several heat cycles. Even the occasional maiden mare will be infected if she is a windsucker , and a complete veterinary examination of the reproductive tract can check not just for infection, but also for injuries and anatomic defects that affect fertility and cycling. For barren mares a full investigation was likely performed at the end of last season and now is a good time to recheck her.

From a nutrition stand point, the critical aspect is her body condition. Mares in moderate to good condition are more likely to cycle and conceive than those that are too thin or grossly overweight. Ideally, at the time she is bred, the mare has been in moderate condition and is adding just a little weight. While many other things will affect your final result, paying attention to these aspects optimizes your mare’s chance of conceiving.

By Scott Madill, DVM
Horse Newsletter (Volume 2, Issue 2)
University of Minnesota Extension Service