For thousands of years, wherever they live in the world, wild horses have been exposed to a constant change in temperature; either by the difference in temperature between day and night, or by the difference in temperature between seasons of the year.
However, even today wild and semi-wild horses — as well as domestic horses — if they have the appropriate living conditions for their species, they can survive in any condition to which they are exposed in mother nature: wind, sun, rain, snow…
Whether it’s Europe, Australia or North America, wild horses are never in search of excessively closed and artificial shelters such as stables, nor do they look for a way to cover themselves with cloth; they naturally evolved ways to thrive and survive in all these conditions.
Let’s see how wild horses biologically manage to survive in winter, but first…
Some historic facts about wild horses
It’s important to note that nowadays, horses living in the “wild” that are descendants of horses that have been domesticated, aren’t really wild horses.
These are known as feral horses.
Many people believe that the only truly wild horse today is the “Przewalski’s horse”. This a native breed from central Asia.
On the other hand, there are also the “wild” horses of the American west, that in reality are also feral horses. These are better known as “Mustangs”.
Mustangs were horses reintroduced in America by Europeans, mainly by the Spaniards or Conquistadors in the 15th century.
Many of these horses were liberated into the wild or that someway managed to escape from their owners; they were able to survive, reproduce and adapt to the wild, and their descendants are now what we see as “wild horses”, but in reality they’re feral horses.
On the other hand, a recent study shows that there are no real wild horses in existence today.
It was believed for a long time that the Przewalski’s horse from Mongolia, was the last wild horse because there were no signs of domestication — contrary to the case of Mustangs.
But the research and examination performed over the genomes of many ancient and modern horses, clearly evidenced that Przewalski’s horse is in reality, a descendant from horses domesticated in northern Kazakhstan more that 5,000 years ago.
A culture knows as the Botai, were the earliest people that successfully domesticated horses, and the actual Przewalski is a descendant from these initial breeds.
Biological factors that help wild horses to survive in winter
There are several natural mechanisms that horses in cold weather use to easily dominate these extreme climates; in fact, it’s easier for a horse to “warm up” in cold weather than it’s to cool down in hot weather, or to cool down after intensive exercise.
1.- The role of the skin
The horse’s skin is one of the main factors that play a role in protecting the internal body from extreme temperature changes, as well as impeding that horses loss too much heat in cold climates.
The first thing to note is that thanks to some thermoregulatory factors such as skin and hair — which are excellent insulators and prevent loss — horses can isolate the heat produced by the muscles through movements.
The skin is also responsible for the dissipation of body heat generated by muscle action to prevent overheating.
Then, to be more detailed, the thermoregulatory mechanism of the skin consists of six major factors:
- Arteries (in skin and legs)
- Respiratory system
- Sweat glands
Five of these factors are responsible for keeping horses warm in cold weather.
We already talked a bit about the role of the skin, let’s see how the coat works.
The fur in horses changes twice a year through the photoperiod mechanism, adapting to different temperatures based on the seasons of the year. Sensors in the horse’s skin react to changes in the duration of daylight.
Horses are ready to grow their winter coat just after the summer solstice, when days start to get shorter and shorter.
The opposite is also true: the coat starts disappearing from winter to summer after the winter solstice, when the days start to get longer and longer.
In addition to the photoperiod, changes in temperature also affect hair growth.
Coat insulation depends on three factors: how much deep and thick is the coat, the speed of the wind, and the internal temperature and humidity of the coat.
In colder climates, horses produce thicker and longer fur than in warmer climates.
There are also other factors that can influence, such as the horse’s diet and breed.
Additionally, this coat can increase the insulation of the temperature through a mechanism by which the horse can raise and lower, or turning the coat in different directions thanks to hair erector muscles.
This way, horses can increase or decrease the thickness of the coat depending on how much insulation they require. This mechanism can increase the deepening of the coat between 12% to 35% in mature horses.
These special erector muscles need to be exercised regularly in order to function properly, the same as other muscles.
Also, the horse’s hair is covered with a greasy substance, which helps the horse to avoid getting its skin wet on rainy or snowy days.
Horses in rain can perfectly repel water thanks to this hair oil; water runs through the outer hair while the deeper layer remains dry.
The thicker the coat, the less water has a chance to reach the skin. If fact, moisture will freeze on the surface of the coat, so it’ll never reach the skin.
The coat also has an extra insulating effect due to small air pockets that get trapped in the hairs, impeding body heat to escape, so snow or rain won’t be a problem for a horse with a good winter hair coat.
Mud has also protective effects on the body.
3.- Arteries in the skin
Horse’s skin can reduce or widen arteries in the skin to regulate superficial blood flow; this is possible due to muscular actions called vasoconstriction or vasodilation.
Constriction prevents loss of body heat by reducing the amount of warm blood that is carried to the surface of the body where it is colder.
Dilation allows a greater amount of warm blood derived by internal overheating to flow, so that it reaches the surface of the body and cools.
Horses also have a powerful circulatory system, which helps in keeping and distributing heat through vital internal organs.
If there is a need to dissipated heat, the circulatory system near the surface of the skin activates with the mechanisms already mentioned, and heat can escape and cool down the horse.
The opposite happens in cold weather: the horse’s organism is naturally programmed to avoid that heat escapes easily, keeping the animal warm.
Some organs in horses are abundantly supplied with blood and are pretty rare to freeze in extreme cold conditions — the muzzle is one of these.
While there are other organs like the ears that doesn’t have enough flow of hot blood because they are pretty thin, so they’ll be more prone to freeze.
The amount of fat in the body is also an important factor in thermoregulation. Since, in addition to serving as the body’s energy reserve, fat is three times efficient as an insulator than other tissues; this is due to its low thermal conductivity and poor blood supply.
For the mentioned reason, it’s very important that a horse has a good layer of fat before winter. Wild horses can naturally maintain the natural rate of weight change throughout the year, usually increasing their weight by 20% in the fall.
Sometimes, it’s possible to see that domestic horses with a great amount of fat on their bodies, grow a shorter winter fur than those horses with less fat gain in the previous season. This is the same for wild horses.
Also, fat is more evenly distributed over the surface of the body in cold conditions, instead of being concentrated in some particular areas such as in hot conditions.
Depending on the horse breed, usually the smaller wild horse breeds have a longer and thicker coat compared to larger breeds.
These characteristics are possible due to the natural change in body proportions; if there is an increment in body size, this affects the heat balance within animal species.
A larger body size provides an advantage on thermoregulation in cold climates.
The ratio of the heat dissipation surface is more efficient to produce or retain heat, when the size of the body increases. Small horses lose more body heat than large ones. Having a spherical body shape influences a lot over this factor.
On the other hand, horses that developed heavier rounded bodies with shorter limbs which are protected by thick hair, a large mane and a greater amount of hair on the fetlock, are able to retain more body heat and cope with the cold without retaining too much fat.
5.- Feet and Legs
Horses have feet and legs specially designed to stand in snow without freezing and chilling their entire bodies. In fact, a horse in snow can easily avoid frostbite in winter.
In fact, horses don’t have muscle masses below their knees. In that area, they mostly have tendons and bones, tissues that resist the effects of cold climates much better than muscle. These tissues require less energy compared with the rest of the body.
Horses have an elaborate system of blood pumping in each foot. The frog, the cushion and the veins around, act like a kind of pump that sends blood back to the interior of the body.
It works as a hydraulic pump each time the horse puts weight on a hoof, creating a cushioning effect that sends blood back to the system very quickly.
6.- Respiratory System
Horses also have a powerful and efficient respiratory system that keep air warm when it passes through the upper airway.
Guttural pouches which are the two cavities at the base of the skull in horses, have a moderation effect on air and this helps to avoid that cold air reach the lungs.
What do wild horses eat in the winter?
Wild horses are animals that never try to shelter themselves. It doesn’t matter how cold it is or if the snow covers the mountain thickly; they prefer to sleep in the open, always in a group, protecting themselves in a herd.
Wild horses will roam large areas of land, grazing and looking for any plant that is ready to eat and nutritious enough. They can survive on a steady supply of grass or any other type of eatable plant.
Some studies show that a horse can graze for about 20 hours (they usually sleep two or three hours) per day if they’re left in environments where there is sufficient foliage for grazing. This is enough to provide wild horses with all of the nutrients they need to survive.
Winter is not an exception. In the absence of food, horses will dig with their feet in the snow to expose the grass that is hidden, and if necessary, they feed on the thin branches of trees even if these don’t have leaves.
While grasses are the type of forage that horses prefer, during winter, horses will eat whatever they find succulent, and shrubs will constitute almost the major portion of their diet.
Regarding hydration, some studies show that as horses are hind gut fermenters, their gastrointestinal tracts are like fluid reservoirs in dehydration and rehydration periods. This helps them to avoid dehydration.
A horse that grazes most part of the day and constantly keep its digestive tract full of food, will have a constant source of energy that will produce enough heat to support the animal during cold climates.
Hind gut in horses are like an internal furnace, thanks to the fermentation process. If they can, they’ll increase the amount of food in their diet accordingly to each increase in the outdoor temperature.