Thermoregulation in horses during the cold season.

Thermoregulation in horses or why horses should not be blanketed or brushed in winter, and should be fed with free access to quality forage 24/7.

By: Natalija Aleksandrova - Holistic Horse & Hoof Care

Most horse owners are aware of the damage and crises

inherent in fever states, but few owners realize how well

adapted their horses are to cope with the cold when provided with the means and environment suitable for their natural lifestyle.

For a mammal to survive, internal body temperature must be maintained

within a very narrow range. If the temperature exceeds these limits, chemical reactions at the cellular level function incorrectly. Or they stop functioning altogether. Fluctuations outside the normal temperature range lead to health problems or death for the animal.

Adult horses maintain their internal body temperature within a range

around 38 ℃. Foals, growing young, pregnant mares and

Infants have a higher internal body temperature (Hines, 2004).

For thousands of years, the wild horse has spread throughout the world.

Wherever in the world they live, the horse was exposed to the

constant variation in temperature through a day/night rhythm or a rhythm

Seasonal. However, even today wild and semi-wild horses, as well as domestic ones, always with the appropriate living conditions, survive.

perfectly in any condition to which nature exposes them. Whether in the

Northern Europe or in the Australian deserts, the horse is exposed to all the

changing elements of nature: wind, sun, rain, snow, temperature

fluctuating, etc. In nature, it has never sought cover, shelter, or stables, or even caves. The horse has evolved and found natural ways to thrive.

Heat in the horse's body is continuously generated as a byproduct of

metabolism, and a healthy animal has significant internal sources of heat from the

metabolic processes (Bicego, 2007). To control internal heat loss

During the cold season of the year, nature has endowed the horse with complicated and

Extremely efficient anatomical, physiological, and behavioral thermoregulatory mechanisms. For these mechanisms to function most efficiently, the horse requires an environment and living conditions appropriate to its species.

At the genetic level, the domestic horse is the same as its wild counterpart, it has the

same abilities and needs to survive. Basically, they don't need anything from humans, other than providing them with the same living conditions as this

species has in nature.

These are the conditions that satisfy all the essential biological needs of the horse and allow it to exhibit its natural behaviors that have evolved to

over several thousand years:

- A herd life and a social life. The horse is a herd animal. Its brain

has different capabilities that the brain of the solitary animal does not have. Only in a

horse that lives in a herd, its cerebral cortex works correctly, giving

normal correct orders for the functioning of other brain centers

subordinates. Only in this way is the horse healthy and psychologically balanced.

-Freedom of movement 24 hours a day. Movement is essential for

horse's metabolism and essential for the health of its hooves.

-Free access to adequate food, fodder, 24 hours a day, whether in

good-quality grass or hay, and of course, fresh, clean water . A horse's stomach secretes acid constantly throughout the day and night, so it must be counteracted with forage to prevent ulcers from developing.

-A shelter that they can enter and exit freely. Whether it is a building or

natural shelters such as trees, forests or hills.

-Optimal care of their hooves. Whether through natural, free-range conditions or proper physiological adjustments.

Under human care that respects and provides for the natural needs of the

horse, and does not make this animal a subject for anthropomorphism through

stables, change of eating habits, shelter with blankets, sheared,

hardware, etc., the domestic horse is able to properly use its incredible

thermoregulatory abilities naturally in exactly the same way as the wild horse.

Let's study in more depth how the mechanisms work

thermoregulators in the horse, and how they are interfered with and damaged by handling and

unnatural care.

First and foremost, it's important to remember that due to thermoregulatory factors such as the skin and coat, which are very good insulators and prevent heat loss, and the muscles, which produce heat through their movements, it's much easier for horses to warm up in cold weather than to cool down in hot weather, or to cool down after intensive exercise. Cooling down is more difficult for the horse. Horses are adapted to handle the cold. A horse's skin is responsible for both protecting the interior of the body from changes in external temperature and preventing heat loss in cold weather.

It should also be mentioned that the skin is responsible for heat dissipation.

internal generated by muscular action to prevent overheating of the

body.

The thermoregulatory mechanisms of the skin consist of four main factors: the skin, the undercoat, the arteries, and the sweat glands, three of which are responsible for keeping the horse warm in cold weather:

1. The skin itself functions as an insulating layer through its relative thickness.

2. The coat. Coat insulation depends on hair depth and thickness, wind speed, and temperature and humidity gradients within the coat (Ousey et al., 1992). The coat, in horses, changes twice a year through the

mechanism called photoperiodism, adapting to different temperatures

Seasonal. Sensors in the horse's skin react to changes in length

of daylight. The horse is ready to grow its winter coat just after

of the summer solstice, when the days begin to get shorter. The horse is ready to change from its winter coat to a summer one just after the winter solstice, when the days begin to get longer. In addition to the photoperiod,

Ambient temperature also affects hair growth. In colder climates,

Horses produce thicker and longer coats than in warmer climates,

compare horses that have the same body score and are given the same

quantity of food.

Coat of an Arabian horse on a very cold winter day (around -27°C/-17°F, Central Europe). The piloerection mechanism is at work, raising the hair to increase the insulation of the coat.

It is also observed that foals are already born with the mechanism that controls the

coat growth. We can see that foals born at the beginning of the

Spring horses are born with a longer coat than those born in late spring or summer. Coat growth is also affected by several other factors, such as the horse's diet and breed.

In addition to growing its hair, the horse can increase the insulation of its coat through a mechanism called piloerection, raising, lowering, or twisting the hair in different directions using the arrector pili muscles. In this way, the horse increases or decreases the thickness of its insulating layer and effectively varies the amount of airflow to the skin surface.

Piloerection increases coat depth by 10% to 30% in mature horses.

The arrector pili muscles must be exercised regularly to work

properly, just like any other muscle in the body. The hairs of the coat are covered with a fatty substance, which helps the horse keep its skin dry on days

Rainy or snowy. The coat has a water-repellent effect thanks to this oily coat; water slides off the outer coat while the deeper coat

Stays dry. The longer the coat, the less water reaches the skin. Through regular brushing, the oily substance is removed and the effect

Water repellent deteriorates. It's also not advisable to clean the layer of dirt that coats the horse when it rolls in the mud. Mud, in addition to protecting against insects, has a cooling effect in warmer climates. Needless to say, the popular practice of clipping a horse's hair completely eliminates the coat's thermoregulatory factor, and shampooing removes the protective oils from the hair, destroying its water-repellent effect.

3. Arteries in the skin. The arteries through muscular actions, called

Vasoconstriction or vasodilation can narrow or widen, regulating blood flow to the skin. Constriction prevents internal heat loss by reducing the amount of warm blood brought to the cooler body surface. Dilation allows more warm blood from the overheated interior to reach the body surface and be cooled. The cooled blood lowers the body's internal temperature when it is returned to the interior.

4. Sweat glands. The horse uses its sweat glands to cool itself when external or internal temperatures are too hot.

When the outside temperature is too high for the air to cool the blood

Through the skin, sweat glands secrete fluid. The evaporation of this fluid

liquid cools the surface of the skin and the blood in the superficial arteries. In this way

way, bringing the cooled blood to the internal body, the temperature internally

It can be lowered even when it's hot outside. The horse stops secreting sweat as soon as its internal body temperature has reached normal. It must then dry quickly, otherwise the cooling would continue and bring its body temperature below normal limits. A sweaty horse turns its coat hairs in various directions to avoid getting too cold, and when at large, it generally looks for a windy spot to dry itself effectively, quickly, and safely. Mentioning the mechanism of the sweat glands is important because sweat glands are also activated by muscular action.

While these are the four main thermoregulatory mechanisms, let's now look at other thermoregulatory mechanisms in horses.

- The lungs. In addition to the use of skin, coat, changes in blood circulation, and sweating as a means of controlling internal temperature, the horse has access to a cooling mechanism involving the lungs. The air exhaled from the lungs contains moisture. In warm conditions, if the above thermoregulatory mechanisms are not adequate to cool the body, the horse may increase its breathing so that more air is taken into the lungs and more (hot) water vapor is expelled, taking heat from the body. Most of us are familiar with dogs panting to cool themselves.

Increased respiration can be an effective way to cool the body, but unfortunately, many horses already breathe more air than is good for them. This is because factors such as stalls, isolation, unnatural feeding habits, blankets, clipping, shoeing, etc., place stress on their physiology, resulting in increased adrenaline production, which is directly related to an increase in the volume of air breathed. Increased respiration has a direct and detrimental effect on physiology (including, for example, a reduction in oxygen availability), which can lead to an inability to function properly and the appearance of symptoms (http://www.equinebreathing.com).

Increased breathing in cold weather can cause excessive heat loss

internal.

Body fat. The amount of fat in the body is also an important factor.

thermoregulation. Since, in addition to being the body's energy reserve, the

Fat is three times more insulating than other tissues, due to its low conductivity

thermal and its scarce blood supply (Guyton, 1991; Davenport, 1992). Therefore

Therefore, it is important for a horse to have a good layer of fat before winter.

Wild horses and domestic horses kept naturally

maintain their natural rhythm of weight fluctuation throughout the year, increasing

their weight up to 20% in the fall. We can usually see that horses

Domestic cats with a thicker layer of fat on their bodies grow a layer of

relatively shorter winter than horses with less fat gain in

autumn, comparing the same breed and the same body weight. Fat is also distributed more evenly over the body surface in cold conditions rather than concentrated in specific areas as in warm conditions.

Body size and shape. Kept in the same conditions, the breeds of

Smaller horses have a longer and thicker coat compared to

larger breeds. We also typically see a thicker coat in foals. This is related to the large effect of allometry, the systematic change in the

body proportions with increasing size and heat balance within

of animal species. Changes within species occur as animals grow and develop, but they also exist between breeds of the same species.

species (Reiss, 1991; Langlois, 1994). Generally, a large body size is

an advantage with respect to thermoregulation in the cold. Since the proportion

The gap between the heat-dissipating surface area and the heat-producing and heat-retaining body mass decreases with increasing body size (Phillips & Heath, 1995; Bligh, 1998). Small horses lose more body heat than large horses.

In addition to the large body size, the spherical body shape reduces the area

superficial in proportion to its body mass (Langlois, 1994) To compensate for the

greater surface area/mass ratio, horses from colder northern areas

They have generally developed heavier, rounder bodies and limbs

shorter ones that are well protected by thick hair, the mane and long hairs on the fetlock, so they are better able to retain more body heat and cope with the cold.

Digestion of fiber. Increasing food intake increases fiber production.

heat in the horse's body. This is related to the fact that the process of

Digestion of long fibers produces heat as a byproduct. It is important that the

domestic horses have unlimited access to forage 24 hours a day. And here it is

It is important to note that all types of slow feeders or slowfeeders that

They prevent the horse from having a bite of hay whenever it wants; they are not completely natural. This form of feeding cannot truly be considered the free access to food that occurs in nature.

In cold weather this access to grass or hay gives them the opportunity to increase the

heat production by continuously eating and digesting long fiber.

Especially when some of the other thermoregulatory mechanisms are not yet

have had enough time to adjust to sudden weather conditions,

such as a rapid drop in temperature.

A domestic horse refreshes its menu with old, dry grass in winter. This can contain high levels of sugars and other nutrients beneficial to the horse.

This additional demand for food is called climatic energy demand.

(MacCormak & Bruce, 1991). It has been observed that horses need

approximately 0.2 to 2.5% more energy to maintain their body temperature

For every 1 degree Celsius decrease in outside temperature below its

lower critical temperature (Young Coote, 1973, McBride et al., 1985, Cymbaluk et

al., 1989a Cymbaluk, 1990). (The lowest critical temperature is individual for each

horse/group of horses at different times of the year and depends on many other

thermoregulatory and environmental factors).

It is important to note that smaller horses have higher values

critical temperatures, which means that their heat loss is relatively

greater than that of larger horses. Thus, small horses

They actually need proportionally more additional food. To explain this better, the higher the lower critical temperature, the greater the heat loss.

experiences the animal. Small horse breeds lose more heat

that large horse breeds under the same conditions

temperature. The lower the lower critical temperature value, the greater the

heat retention experienced by the animal. The larger breeds of horses

stay warmer in cold weather.

Reduced activity in cold weather. Wild horses have been shown to

reduce their locomotor activity in winter compared to summer (Duncan,

1980, Berger et al., 1999, Arnold et al., 2006). Reduced activity in winter was an annual pattern associated with decreased outdoor temperature and, consequently, reduced internal heat production and energy expenditure (Arnold et al., 2006). This adaptive mechanism of reduced activity helps wild horses cope with the energetic challenge of winter.

We can observe a similar reduction in winter activity in horses.

Domestic horses kept in natural conditions. However, domestic horses do not face the challenge of foraging in winter to the same extent as their wild counterparts. This slowdown in activity obviously serves the same purpose as in wild horses: reducing energy expenditure in the cold. Therefore, it is a normal seasonal rhythm for horses to move less in winter due to their thermoregulation mechanism in response to the cold, so it is not advisable to force horses in winter.

Short bouts of activity in the cold. Along with the general reduction in activity during the cold season, we have observed short bouts of restlessness and locomotor activity (movement) in horses during periods of sudden cold.

acute and adverse weather. Beneficial short-term movement that is a useful bridge

until other factors of your thermoregulatory system adjust to the new

temperature conditions.

Reduce heat loss and gain heat through body radiation. Sometimes

We can observe horses standing or lying very close to each other, thereby reducing heat loss through radiation. Through this positional proximity to each other, they reduce the body surface area exposed to the external environment (Bligh, 1998). At the same time, animals that for some reason do not produce enough internal heat individually can use the radiation of body heat from a paddock mate as an additional source of beneficial heat.

Sunbathing. Horses also change their body posture and orientation.

It can increase absorbed solar radiation to use as an additional source of heat. We can often observe that horses prefer to bask in the sun.

directly instead of eating during the short sunny winter days, and so

as soon as the sun sets again to eat.

Sunbathing on a winter day.

Snow on the back. The snow we sometimes see on the backs of horses.

During the winter it also plays the useful role of providing a protective layer

additional protection against internal heat loss.

Body position and posture. On windy and rainy days, we may see horses standing with their tails in the wind and their heads low. In this way, they effectively keep their necks, heads, ears and eyes, belly, and hooves out of the water and wind. Their tails serve to protect their hind ends, the shorter hairs of the

maslo act by deflecting snow and wind. Also on those days, horses

They can be seen standing next to walls, or using natural windbreaks, such as trees or hills to protect themselves from the wind.

When allowed to choose, horses have been observed to use the spaces

closed, such as shelters or forests, more to hide from the summer heat and

flies, not wind and rain.

Shivering. In extreme circumstances, the heat in the horse's body can be

generated by shivering. During shivering, heat is produced rapidly by

break down ATP in the muscles (Langlois, 1994). Tremor is usually a

acute response to sudden exposure to cold, or sometimes occurs over periods

prolonged exposure to cold in rainy weather. In healthy animals, shivering is replaced by normal internal heat production as they adapt to the new climatic conditions.

Thermoregulation in the hooves. A constant temperature in the hooves is

necessary for the proper functioning of the metabolism, which together with other

factors, allows for normal hoof production. The hoof capsule has

Insulating properties. Through the specific expansion and deformation mechanism and its internal structures upon impact, energy is created that releases heat as a byproduct, thus keeping the hoof warm. For the hoof mechanism to function properly, a horse needs unrestricted hooves and unrestricted movement throughout the day and night. Horseshoes affect the hooves' ability to maintain this constant temperature by blocking their ability to expand and deform properly upon impact. Hooves also conduct cold internally. We can often observe snow forming balls on the soles of shod horses, where it normally melts on healthy, unshod hooves.

Horse Blankets. Covering your horse with a blanket can take its

thermoregulation to a complete disorder. The animal tries to warm parts of the

body parts left exposed to the cold, such as the head, neck, belly and legs, and in the process the parts covered by the blanket become overheated. A horse cannot

increase the heat in a selected area of your body. The entire body cools or

The whole body heats up. Sweating under a blanket is a metabolic problem.

serious for the horse than people think.

Stalls and blankets. A different problem occurs with enclosed spaces, when a hot, sweaty horse is placed in a stable. Due to the lack of air circulation, cooling takes longer and the horse sweats for longer. The air surrounding the horse

horse becomes saturated and drying also takes longer than normal, because the humid air

cannot absorb any more moisture. As a result, the horse remains under

cooling, creating the conditions for an internal disorder: colic,

diseases and infections by negatively affecting temperature margins

safe metabolism.

Kept in boxes or covered, horses lack stimuli (fluctuations in

temperature) that stimulate the activity of thermoregulatory mechanisms. No

need to exercise the arrector hair muscles, nor to dilate or narrow the

arteries, nor to activate sweat glands, nor to prepare or deplete healthy fat reserves. All muscles atrophy without exercise over a period of time. If an animal in this state is suddenly exposed to cold, they will be unable to activate the necessary thermoregulatory mechanisms. As a result, the internal body temperature could drop too low, leading to disruptions in metabolic processes. This can affect, for example, the rate of production and migration of white blood cells and antibodies, resulting in their partial inability to function.

The result is a stressed animal with a disease or infection harbored in its

internal environment. The germ is nothing, the environment is everything (Louis Pasteur).

Consequently, germs or viruses in the body have a chance

perfect for breeding.

Effects of stress. In addition to the fact that thermoregulatory mechanisms

Natural abilities can only be fully utilized when a horse is kept in the

living conditions appropriate for their species, there is a factor of anxiety and stress

that horses inevitably experience when deprived of their basic needs and kept in unnatural ways (stalls, separation from fellow horses, forced exercise, lack of consistent fiber intake, etc.). This stress also makes them less able to cope with the cold. We know all too well that stress weakens the immune system.

Strengthen your horse's immune system by giving it the life it was meant to be!

designed by nature!

by ©Natalija Aleksandrova

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