Using lights to regulate your horse’s hair coat


Using lights to regulate your horse’s hair coat is a surefire way to do a few things in your barn – prevent winter coats from coming in, keep your mares cycling throughout the winter, and cause a hefty electric bill.  But in some cases, lights work well.  


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The science of light and hair growth


  • A horse’s eyes, specifically the photoreceptor cells in the eyes, notice when daylight hours start to increase and decrease in the spring and fall.  That relays a message to the brain, letting your horse know it’s time to shed one coat and grow another. 


  • It’s a MYTH that temperatures control hair growth.  The perfect example is a wooly mammoth horse like a Fjord that lives in Key West, still growing a giant winter coat.  


  • Light also controls the estrus cycle of mares.   In times of shorter daylight hours, the cycle ends.  Breeders may keep the lights on to trick horses into estrus, thus making the breeding and foaling cycle more adjustable. 


  • Some barns choose to keep horses under lights for coat control. Horses under lights won’t grow a winter coat, so you avoid clipping and the funny colored hair that sometimes results from clipping.


Read more about how horses know when to shed and grow a new coat


How much light do you need to add?



  • Recent research from my alma mater, Texas A & M, has concluded that 16 hours of daylight (synthetic and natural) are needed to prevent horses from growing a winter coat.


  • You will have the best success if you do two things – keep this routine year-round, and use “full spectrum” lighting. This is a fancy way of saying fake sunlight. Full-spectrum lights are available at most hardware stores and cost more but mimic natural light.


  • Mares will also continue to cycle throughout the winter, which may or may not be something you are interested in.



barn at night with lights on

A barn in CA that keeps the lights on until about 10 pm. They pop back on at 5 am. Year-round!  No winter coats here.


  • I know barns that use lights and are set on a schedule to extend natural daylight. The lights are turned on at 5 am or so, off when it’s naturally light, on again before dusk, and off at 10 or 11 pm. Timers are great for this task, but you will need to adjust the timers every few weeks as the days lengthen or shorten.


barn aisle lighting

Barn aisle lights are not enough… Ideally, each stall should be illuminated.



safe light in cage

These won’t do the trick for stopping winter coats, but I like them because they are covered with a cage for safety.


  • Now – you may be wondering if a little 100W bulb will do. Probably not. You should count on at least two 8′ tubes of lights per 12 x 12 stall. These types of lights usually come in 4 or 8-foot sections. Easy to install! Be sure your tube lights have a cover on them, just in case.


  • You will also have to blanket your horse if you use lights to regulate your horse’s hair coat, as his summer coat likely won’t keep him warm in the winter.




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