Stadium style lights help recipient mares to cycle in Oklahoma. * Photo by Katie Houck

5 Tips For Putting Your Mare Under Lights

If you live in the Northern hemisphere and are active in the Western performance horse world, you likely already know that your stock horse automatically ages up a year every January 1. If you’re trying to produce a prospect for the cutting, reining or reined cow horse futurities, it makes sense then that you’d want it born as close to the beginning of January as possible to give it an advantage in growth and training over other horses born later in the year.

Unfortunately, mares, who have an 11-month gestation period, don’t naturally start ovulating until about April, meaning the earliest they’d be able to have a foal without any assistance is in March. For years, though, breeders have found a way to combat this and bring mares into estrus sooner by using artificial light to trick their bodies into thinking spring has arrived. It must be done a certain way, but it is generally a successful technique as long as the proper protocols are followed.

Quarter Horse News spoke with Dr. Bianca Casa at Outlaw Equine, based in Decatur, Texas, to learn how to use this method appropriately for breeding mares.

Even on the shortest days these recipient mares have 16 hours of lights. * Photo by Katie Houck

Leave Lights on for 16 Hours

During fall, decreasing daylight causes mares’ bodies to produce more melatonin, suppressing ovarian activity. By the time winter arrives, most places in the United States experience significantly shorter days with often 10 hours or less of daylight. In order to breed your mare before the start of spring, you will need to extend that daylight period artificially to where she is getting 16 hours of light and eight hours of darkness each day.

“All mares usually cycle whenever we have an increased number of daylight hours,” Casa said. “If you’re looking to breed your mare anywhere from January until March, we need to stimulate them by putting them under lights, which we call artificial photoperiods.”

The hours of darkness are just as important as the hours of daylight, and leaving the lights on 24 hours a day can actually be less effective. Therefore, you might put your barn’s lights on timers, saving yourself the hassle of trekking back and forth to the barn in the middle of winter.

Start After Thanksgiving

Once a mare is under lights, it will take 60-80 days before she starts cycling. That means for a mare to be ready to breed in early February, you will need to start putting her under lights by the end of November.

“I always tell my clients to start extending the light period a day after Thanksgiving,” Casa said. “That timing is going to give us until the end of January and beginning of February for those mares to start cycling. We usually don’t see results before 60 days at all.”

Make Sure Your Lights Are Bright Enough

Not just any lights will do the trick — lights that are too dim will not cause your mare to start cycling. The general rule of thumb is you want to have enough light that you can read a newspaper in a 12 by 12 stall. Casa recommended bulbs that equal around 200 watts, regardless of color and warmth. They can be LED, fluorescent or incandescent, as long as they are bright enough.


A word of caution — mares that are under lights but can hang their heads out into dark barn aisles or through open exterior windows can actually negate the effects of the extended light periods. If a mare cannot actually see the light, her body won’t respond to it. Therefore, it’s important to close exterior windows and either light the aisleway or close the top of her stall door so that she’s continuously viewing light.

Leave Mares Under Lights Until Spring

Casa recommended that broodmares follow the 16/8 daylight schedule until it’s time to set clocks forward in the spring. Even if a mare starts coming into heat in early March, supplemental lighting should be continued until natural daylight hours increase to 14-16 hours a day.

If you stop extending the light cycle too early, or even if you miss a few days, you’ll likely find your attempt at putting your mare into estrus early unsuccessful. By that point, it will be too late to breed her early in the year, and you’ll likely have to wait until she naturally starts ovulating in March or April to breed her.

Pregnant Mares Can Benefit

If your mare is due to foal out during wintertime or early spring and you’re hoping to rebreed her either on her foal heat or the cycle right after, Casa recommended putting her under lights, too. This is because mares that give birth during winter without exposure to extra light will have limited ovarian follicle development, preventing them from being rebred for several weeks.

“After they foal out, sometimes they have too much melatonin in their bodies,” Casa said. “They need to be able to cycle, and we want to breed them as early as possible. Most of these mares just kind of shut down whenever they foal out during that time if they are not under lights, so we encourage clients to put them under lights to avoid this problem.”

There is no need to add extra lighting for mares due in April or after. Keep in mind, though, if your mare is due to foal during the first week of January, exposure to extra light can set her delivery day back a full week. This would mean that her foal could be born in late December, making it automatically a year old on January 1. As this would be devastating for futurity hopefuls, it is advised to use caution when supplementing light for mares due at the beginning of the year.