Horses evolved in the harsh climate of North America's continental divide where winters are bitter cold and summers simmering hot. From this land of their beginning they migrated over the face of the earth. They can be found from the frozen tundra of the Arctic Circle to the fierce heat of the African Sahara. Horses are probably the best weather-adapted animal on earth.
The reasons for this adaptation to extreme cold are, like evolution, complex and myriad -- buried deep in the immortal "selfish genes" that make up the DNA of today's horse. Horses, wearing their home-grown fur coats and feet encased in impervious hooves with sub-solar vascular heating, will survive in temperatures down to 40° below zero, while we naked humans would succumb to frostbite and death at temperatures barely below freezing. But, because we anthropomorphize, we think our horses like what we like, so we generally keep them too warm.
Your horse, unless you clip him, does his own winterizing. He grows a thick fur coat that is all but impervious to cold, wind, rain and snow. Your job is to provide the environment, the care, the feeding and exercise to keep you horse winter-healthy.
Shelter. You don't need a draft-free barn with central heating. Horses don't mind rain, wind or cold, but if the three are combined they do head for shelter. If no shelter is available, they turn tail to the wind, lower their heads, shiver to keep their body temperature normal (100°) and ride out the storm.
Do not consider it inhumane to leave horses outside provided that they are in an environment that allows them to exercise to stay warm, has a wind break, and an elevated place to stand where they are not up to their knees in a soup of mud, manure and urine. A wind break and some kind of shelter is more important in especially cold weather that is combined with rain/snow and wind to help prevent wind chill.
To clip or not. If you are a pleasure rider, not competing in winter events, don't clip. Your horse is so sensitive to climate and temperature that he will grow the amount of hair needed. Normally he grows hair in the fall and sheds it in the spring. And he will have mini-changes in his "wardrobe" all during the year, with minor shedding and re-growth depending on the length of day and temperature changes.
It is a myth that you can't compete on an unclipped horse. You can but you'll be treated like a guest showing up at a formal wedding in blue jeans. If you are racing, you almost have to clip your horse, for not to do so would be like a runner competing in sweats.
There is a valid reason to clip the endurance horse who sweats heavily and dissipates his body heat more efficiently without his winter overcoat. With a strenuous workout in cold weather your horse's sweat will take a long time to dry. This is OK as long as you cool out your horse -- resting temp (100°), pulse under 60 beats per minute, and respiration below 20 per minute.
Blanketing. Does it help to blanket a horse in pasture? No -- if your horse is not clipped, because the blanket will compress his natural blanket of long hair and upset his natural thermostat. Yes -- if your horse is clipped and the weather dry. But no -- if it is raining, for there are few blankets that will stay dry and help contain the horse's body heat. Even heavy rugs allow water to under-run them. And it is worse to have a soaking blanket on a wet horse than none at all.
Also, there is a clear danger of a horse developing very sore withers and spine from a heavy blanket left on too long, to say nothing of the secondary problems of fungus and bacterial infections. (The clipped horse, often shampooed and "fly wiped," is a "hot house" critter in all seasons, and has many more skin problems than the unclipped, hosed down, and often curried horse.)
Feed. With cold weather you exercise your horse less, which burns fewer calories. But your horse, like your home, has to turn up the thermostat to stay warm. Depending on the weather, your horse may require 50% more calories than normal to keep up his weight and fat insulation. Increasing roughage intake, such as hay, works well as horses can intake more calories over time. Corn oil is an excellent source of calories, though hay is recommended as more "heat producing" (I'm still chewing my cud on this one).
Water intake. Water intake is essential during the cold winter months as dehydration is more common this time of year due to decreases in water consumption. Unfrozen, even warmed, water will increase hay intake and stimulate water intake.
Remove shoes. With fall rain and soft ground, unless you are riding your horse regularly, have your farrier remove the shoes and give him a "natural" barefoot trim. Unless your horse has soft or brittle hooves, he will get along fine without shoes. And, if you want to take a long trail ride, put on hoof boots, and he should be fine for an all-day ride. Going barefooted gives the hoof and frog a chance to grow out normally, away from the constriction of hoof-binding steel shoes.
Hoof abscesses. If his hooves are exposed to long periods of a "corral soup" of mud, manure and urine, he may go lame. Check the bottom of his feet for any signs of black spots, little bubbles of gas or black pus along the white line -- that area of the sole where the hoof wall and the sole join. If infection is present, it goes under various names of white line abscesses, gravel, seedy toe, or foot rot. Call your veterinarian.
Pastern inflammation. This is a continuum which begins with a mild rash called mud fever and, if untreated, can progress to a more severe condition we call scratches.
Mud fever. In very wet weather, bring your horse in occasionally, hose off his legs and hooves, and check for any signs of skin irritation in the pastern area (on the back of the leg, above the hoof). Any redness, irritation, and pain is a sign of "equine diaper rash." Dry the leg and treat it liberally with cornstarch -- as you would your baby's bottom. (It is the same condition, with the same cause, just a different location.)
Scratches. If you have failed to treat your horse's legs during the initial stage of inflammation, the skin will eventually get devitalized, begin cracking and allowing opportunistic bacteria, fungi and yeasts to invade the skin and underlying tissues. At this stage we call it scratches. It may now be so painful that your horse will be lame and reluctant to let you clean and treat it. Treatment: clean and dry the affected area and apply salves like Bag Balm, Desitin or a "cure all" containing vitamins A and D, triple antibiotic and prednisone. Scratches is actually a syndrome that may have many causes, some of which are mixed infections, vasculitis, allergic reaction, etc. If your horse does not respond to the salves in a week, call your vet to get a definitive diagnosis.
Dermatophilosis. This is a nasty skin infection caused by a bacterium called dermatophilia (literally, skin-loving). It is an opportunist that invades devitalized skin and, in severe cases, causes large, thick, hard scabs that are impossible to remove without sedating the horse and prying them off. These lesions may arise anywhere on the body where the skin has been devitalized. Treatment: Sedate, remove scabs, scrub the affected areas with Chlorhexidine or Betadine scrub, apply ointment as for scratches, and inject penicillin as prescribed by your vet.
Rain rot appears as a loss of hair along the top of the back, especially in old, thin horses. It is caused by devitalized circulation in the skin from long exposure to the elements of cold and rain, allowing growth of a bacteria that acts like a fungus (in the way it affects the skin -- rough and hairless).
Problems in the spring. White line abscesses, scratches and rain rot often strike when the weather gets better in the spring. Reason: Accumulation of the long winter's exposure, and now the problems become manifest just when you are getting ready to ride. (Darn!)
Diseases of inactivity. Especially for the horse living in the comfort of the box stall. He will tend to get stiff with stocked-up (swollen) legs, and even lame from lack of exercise. Any arthritis will be exacerbated. He will be more prone to colic (bellyache). He will be more susceptible to respiratory diseases because of the diminished fresh airflow in the confines of the barn.
The old horse. His teeth are bad, his hair coat is extra-long, he may be skinny and have poor fat insulation, and be bordering on Cushing's syndrome. This old fellow, if you are to keep him comfortable, needs special treatment and housing. Work with your veterinarian on this one.
Pasture or stall? There is no doubt in my mind that, in weighing the benefits versus the risks, the winter-pastured horse comes through healthier than the stall-confined animal. But it's not always either/or; if you have both stall and pasture, your horse has the best of all worlds.
Exercise. There is no reason to alter your riding routine because of weather. Your horse can take it if you can. But I do believe you should curtail riding in the winter, to give your horse a vacation and a time for rest and rehabilitation from the rigors of competition. It will do wonders for his mind and body -- and yours -- and will prove to you that, even in the absence of drugs and additives, the body is self-regulating and self-healing.
After a winter's vacation it will not take long to bring a previously well-conditioned, seasoned endurance horse up to condition. Younger horses and horses that have not been previously well-conditioned and competing in endurance riding will take longer to get back in condition.
Doc Steere's mantra: You and your horse are exercise-dependent for health.
During the cold winter months it is important to provide the basics of adequate food/calorie intake; clean, unfrozen water and adequate protection and shelter from the elements. Your horse will thank you and come through the winter months ready to start up again as you and the weather get going.