When the temperature drops, most of us reach for a blanket for our horse before we reach for our own coat. The research suggests horses are tougher than we think, and that the things that really matter in winter are not always the ones we worry about.

Horses evolved on open, windswept grasslands, and a healthy adult with a full winter coat can handle far colder air than its owner. But cold still costs them. It burns energy, it changes how much they drink, and wind and rain can undo a good coat in minutes.

Here is what scientists have learned about how horses cope with cold, and what that means for how we care for them.

How horses stay warm

Every warm-blooded animal has a thermoneutral zone: a range of temperatures where it can hold its body temperature without spending extra energy. The bottom of that range is the lower critical temperature. Below it, the horse has to burn more fuel to stay warm.

That number is not fixed. Swedish researcher Karin Morgan estimated a thermoneutral zone of roughly 5°C to 25°C (41°F to 77°F) for horses in her climate-chamber studies. But horses acclimatized to winter in northern Canada had a lower critical temperature closer to −15°C (5°F). The difference comes from coat, body condition, age, breed and how long the horse has had to adapt.

Horses have three main tools for staying warm:

The winter coat. Longer hair traps a layer of still air against the skin. Tiny muscles can lift the hair to make that layer thicker — the horse's version of goosebumps.

Body fat. Fat under the skin insulates and stores energy to burn for heat.

The hindgut furnace. Microbes in the horse's large intestine ferment fibre, and that fermentation gives off a great deal of heat. A belly full of hay is, quite literally, a built-in heater.

If those are not enough, the horse will shiver. Shivering is a sign it is working hard to stay warm.

What cold costs a horse

More calories. Once the temperature falls below a horse's lower critical temperature, its energy needs climb. The widely used guideline from the U.S. National Research Council is that a mature horse needs about 2.5% more digestible energy for every degree Celsius below that point. At 10 degrees below, that is a quarter more feed. A horse that is not given the extra will burn its own fat and lose condition, often under a coat thick enough to hide it.

Less water, more colic risk. Horses tend to drink less when the water is near freezing, and dry winter hay holds far less moisture than grass. Low water intake is considered a leading factor in impaction colic, the type most often seen in winter.

Wind and wet. Cold air on its own is rarely the problem. Rain flattens the coat and destroys the insulating air layer, and wind strips away body heat. In Norwegian field studies, horses chose to stay outdoors 88% of the time on dry days below 0°C, but only 52% of the time on mild days with wind and rain. The only shivering researchers saw was in mild, wet weather, not in deep cold. A drizzly 5°C day can be harder on a horse than a dry −20°C one.

Which horses feel it most

Breed plays a part, but the individual horse matters more. In one Norwegian study, small warmbloods chose to stay outside only about a third of the time, while small coldblood horses stayed out 80% of the time. But body condition and coat weight also predicted which horses sought shelter. As researcher Grete Jørgensen put it to Equus, a fit, well-muscled Arabian with a thick coat may cope better than an old, thin, clipped Icelandic horse.

The horses that need the most attention are:

Clipped horses. Clipping removes the coat's insulation, so a blanket has to replace it.

Older horses. Dental problems and metabolic conditions can make it harder to eat enough and hold weight.

Thin horses. Less fat means less insulation and fewer reserves to burn.

Foals and young horses. They have a higher lower critical temperature than adults, so they feel the cold sooner.

Horses new to the climate. A horse shipped from a warm region in late fall has not had time to grow a full coat or adapt.

Sick or injured horses. Illness drains the energy they would otherwise use to stay warm.

How to help your horse through winter

Feed more hay, not more grain

When it gets cold, the best extra fuel is forage. Fibre fermented in the hindgut produces far more heat than grain does, which is why nutritionists recommend free-choice, good-quality hay as the simplest way to meet a horse's higher winter energy needs. Before a cold snap, add hay. Grain may help a hard keeper hold weight, but it will not warm a horse the way hay will.

Warm the water

This is one of the best-supported winter studies in horse care. Researchers at the University of Pennsylvania's New Bolton Center found that during cold weather, ponies drank about 40% more water when it was warmed than when it was near freezing. There was a catch: when ponies could choose between warm and icy water, most drank from the cold source, and drank less overall.

The practical takeaways:

Use a tank or bucket heater so water never freezes.

If you can't heat it continuously, top up buckets with hot tap water at feeding time. Most drinking happens within about three hours of a meal.

Offer warm water as the only option, not alongside a cold one.

Soaked hay cubes, beet pulp or a sloppy mash add extra water to the diet.

Give them a way out of the wind and rain

Horses use shelter mostly to escape wind and rain, not cold itself. A Belgian study of 426 horses on 166 pastures found shelter use rose on rainy, windy days, whatever the temperature.

Shelter design matters too. In a Danish study of Icelandic horses wintering outdoors, groups whose run-in shed had two entrances used it significantly more, and horses with only one entrance had higher levels of a stress hormone. A second doorway lets lower-ranking horses get in without being trapped by a bossy herdmate.

Blanket for the weather, not the calendar

Some of the most charming research in the field comes from Norway, where scientists taught 23 horses to "ask" for a blanket by touching boards painted with symbols. The horses consistently chose to go without a blanket on fine days and asked for one when it was wet, windy and cold. On one rainy 9°C (48°F) day, 10 of 12 unblanketed horses asked for a blanket.

A follow-up study found blankets helped but did not replace shelter. Even horses wearing blankets still went inside, especially when rain and wind came together.

So when should you blanket?

Yes: clipped horses, older or thin horses, horses not acclimatized, and any horse in cold rain or sleet without shelter.

Probably not: a healthy, unclipped horse with a full coat, good body condition and access to shelter on a dry, cold day.

Watch for overheating. Sweat under a blanket chills a horse once it dries. Check by sliding a hand under the blanket at the shoulder; it should feel warm and dry, not damp.

Check body condition with your hands

A winter coat can hide weight loss for weeks. Once every week or two, run your hands over the ribs, along the topline and over the hindquarters. If ribs feel easier to find than they did in the fall, add hay and talk to your vet or a nutritionist.

Riding in the cold

Winter riding is mostly about sweat. A horse with a full coat that works hard will sweat into that coat, and wet hair loses its insulation just like rain-soaked hair does.

Warm up longer. Give muscles and joints extra walking time before asking for real work.

Use a quarter sheet on clipped or thin-coated horses during warm-up.

Cool down fully. Walk until breathing is back to normal.

Dry before turnout. Throw on a wicking cooler and wait until the coat is dry, especially at the neck, chest and flanks. Never blanket over a damp coat and walk away.

Consider a clip if your horse works hard all winter and is always sweating. Trace or bib clips remove hair where horses sweat most and leave the rest of the coat to keep them warm. A clipped horse will need a blanket.

Cold snap checklist

When the forecast turns bitter, run through this list:

Extra hay on hand, and fed before the coldest nights.

Water heaters working, or a plan to top up with hot water at every feeding.

Salt available to encourage drinking.

Shelter clean, dry and easy for every horse in the group to get into.

Blankets checked for fit, rips and dampness.

A hands-on body condition check on each horse.

Manure checked for dry, small piles — an early sign a horse isn't drinking enough.

Your vet's number saved, in case of colic.

The bottom line

Horses are built for cold far better than for wet and wind. Keep the hay coming, keep the water warm and unfrozen, give them a way out of the weather, and blanket the horses that truly need it. Most of all, watch your own horse. As the Norwegian researchers found, every horse has its own idea of what "cold" means.

This article is for general information. Every horse is different, so talk to your veterinarian about your horse's winter care, especially if it is older, has a medical condition or is losing weight.

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