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  • Writer's pictureThe PFERA Team

Get ahead of the game

Mares are polyestrous and have multiple heat cycles throughout the year, but a mare’s reproductive tract is normally in anestrous (not cycling) during the fall and winter months. A mares body knows to enter this state by responding to the temperature drop and a decrease in daylight, indicating shorter days. Mares require approximately 16 hours of light and 8 hours of darkness in order to maintain reproductive function (Wright, 2016). You can see why the 10 hours of light the Northern Hemisphere gets in the winter puts the brakes on breeding. With this knowledge, it is reasonable to assume that should you alter her environment, you would be able to bring a mare into an early estrous.

This is where supplemental lighting comes in. Putting your mare under lights is not a new trick, but there is a reason it is still a common practice. Lighting can be an effective way of jump-starting your mare’s cycle by manipulating her body into thinking we are coming out of winter and into the spring. When light registers in the mares retina, it signals her body to suppress melatonin production, creating a domino effect on multiple hormones and ultimately leading to follicle stimulation and development (Roberts, 2015). Using artificial light to encourage your mares cycle is helpful in saving time if you want an earlier foal and to account for pre-breeding management practices. When planning to breed you should remember that not only does the winter leave a mare starting from square one, transitional heats as we enter spring can waste a significant amount of time with unsubstantial follicles and irregular cycles.


  • Start supplemental lighting early! Your mares should be under lights beginning in late November/ early December as they require 30-90 days of photo-stimulation to begin their first estrous cycle

  • Make sure your mare can actually see the light. For artificial light to be effective, it has to register with the mares eyes. Mares should not have the ability to stand in a shadow, hang their head out a window, or over into the barn aisle.

  • Use a timer to maintain consistency and maximize results


  • Forget to leave the lights on! If you miss nights you are not helping your mare respond and adjust to the “seasonal change”

  • Waste your time using dim lights. Lights of 100 watts are usually sufficient to induce photo-stimulation.

  • Cease using lights when you see signs of heat. To keep your mare moving forward, her environment must continue on an upwards trend of daylight increase.

Beware You can put pregnant mares under lights to induce a rapid cycle post-foaling but there is a risk of early foaling. You may want to put a pregnant mare under lights if she is foaling early in the year and you are hoping to breed her back soon afterwards. With temperatures quite low in January/February it could be months until her body regulates a normal heat cycle. Be cautious if you’re considering taking this route, especially if your mare is already known to foal ahead of schedule or if your breed registry requires a D.O.B after January 1st.

If using lights, don't forget to track your mares cycle with teasing and periodic ultrasound scans to make sure she is progressing. Some mares are more responsive than others and we know you're not interested in donating to your hydro company. After inputting tease scores and ultrasound results into FoalPoint, the graphing tool will take your logged info and give you a visual reference to follow cycle regulation. Supplemental lighting can give you a head start to the breeding season but FoalPoint makes that head start worthwhile.

Citations: Roberts, C. 2015. Reproduction: pregnancy diagnosis and early stages. Equine Health. Wright, B. 2016. Artificial lighting for mares. Ontario Ministry of Food and Agriculture.

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