Horses are much better adapted to the cold weather than we give them credit for. They grow an excellent winter coat that insulates them and keeps them warm and dry down to the skin. Horses are healthier if given plenty of outdoor time, which allows them to adjust to the temperatures and lets them breathe fresh air.
HARDY WILD HORSES
Look at horses in nature. In the fall they put on extra weight so they have fat reserves to burn to keep warm in the winter. In winter the main food available for horses is roughage, dead or dormant grasses and weeds. Roughage, and that includes hay, actually helps warm the horses because it releases heat as it is digested. Have you noticed that your horses eat more hay on very cold days? They are keeping warm. So our wild horses eat roughage and often lose weight during the winter, but they survive well and are ready to gain weight rapidly in the spring. In nature, horses stay warm by moving around, since they often have to travel to get unfrozen water. We all know how exercise keeps us warm; just clean your barn to find out.
OUR BARN BUDDIES
Most modern well-kept horses have plenty of hay to keep them warm on a cold day and shelter from the wind and rain (either in the woods, shed or barn). It is good to give them more hay on a cold night, or at least the choice to eat more. But if your horse is in a closed up barn where it's 40 degrees inside, he does not need extra hay. Outside horses with a round bale often do not move much; they leave the round bale only to get water (at least that is what my lazy beasts do). Every now and then, however, horses will run around for no apparent reason ... the reason actually is to get warm. Then they go back to eating.
LOOK AT THE PHOTO
The unblanketed horse’s fur works by insulating him. His body heat is not escaping; if his fur did not work the snow would melt immediately. The unblanketed horse has the same amount of unmelted snow on his back as the blanketed one. Horses can have icicles hanging off their fur and be perfectly warm underneath.

Ellen Haight
Horse covered in snow
Horse covered in snow
SO BLANKETS OR NO?
There are a few reasons to use blankets and a bunch not to. Horses who are clipped need to be blanketed, since we have taken off their fur. Old horses who cannot keep warm need blankets, even if they never needed them when they were younger. Horses who have been sick, are too thin, have been rescued or have any other health problems may need blankets. Some individuals of any age are cold-natured and really do need to be blanketed, as do horses who have no shelter. The rest of the unclipped population does not. How many blankets do horses need? In most cases a single blanket will do the trick, with heavy blankets being used in the cold weather. You can stick your hand under the blanket and if it is toasty and warm, it is heavy enough for the weather. If it feels cool under the blanket, you may need a heavier one. Please do not get a great fitting outer blanket and add an old-fashioned design sheet underneath. The sheet does not add much warmth, and it usually rubs the shoulders and causes a lot of pain. Remember that a horse's fur fluffs out when it is cold. This adds air space (like your down jacket) and that air fills with warmth making the fur more efficient. Blankets crush down that air space, so you need a heavy enough blanket to provide true warmth. A thin sheet may protect a horse from rain, but it may not provide much warmth and may leave the horse colder than if he had no blanket. If you choose to blanket and start early in the season you will need to keep it up, since the horse will adapt to wearing it, and his temperature regulation will be accustomed to it.
TESTING FOR WARMTH
How do you tell if your horse is warm enough? You have to get to know your horse and pay attention to small behaviors. Horses who are cold tend to huddle up in a sheltered place and may not be willing to go out into the pasture area even to eat hay to keep warm. They may really crave their stalls. They may shiver excessively. While shivering is a perfectly normal way to warm up, the cold horse will be seen shivering much more frequently or when all the other horses are not.
SWEATING
Clipping a working horse in the winter becomes a necessity when you work hard enough for him to break a sweat. Sweat adds moisture from the skin out, which means the dry fluffy fur cannot work. Horses will get very cold if not dried off completely after working. You cannot put a blanket on a warm or hot horse as they will just sweat more. What about those times you leave for work at 5 a.m. when it’s 15 degrees out, and by noon it’s 60 degrees? There is no magic blanketing solution. Perhaps you can recruit a friend to stop over and take blankets off later in the morning, or put on a lighter blanket for the day; it may not be perfect, but it would be more comfortable than being too hot for most of the day. There is no temperature where it is too cold for a horse to be outside if they are adapted to it. So let your horses enjoy the cold weather, and go out for a winter ride.
Joyce C. Harman, DVM, MRCVS, operates Harmany Equine Clinic, Ltd. in Washington, VA. Acupuncture, chiropractic, homeopathy, herbs, nutrition and saddle fitting make up most of the practice. www.harmanyequine.com