When do horses feel the cold? Vet explains at what point they might need a rug

Knowing when horses feel the cold and, consequently, when to rug is something that sits almost permanently in the mind of many a horse owner.

When the temperatures start to drop and the forecast is wetter, it can be tempting to reach for that massive, all-in-one heavyweight turnout rug to keep your horse nice and toasty – but in the back of your mind, you know that vets have warned about the dangers of over-rugging.

If you’re deciding whether to rug your horse, you could consult our rugging temperature guide for a quick answer, but it’s important to know at what point your individual horse is actually feeling the cold. To be sure you’re doing the right thing, you need to consider and understand how nature has equipped him (and the rest of his species) with some unique tolerances to cope with cold, wet weather and changing seasons. Vet Ricky Farr explains why some horses may need a rug sooner or later than you might have thought.

How horses have adapted

Horses are found throughout every climate on the planet, from the sub-zero north to the tropics and arid deserts. Their adaptations that allow them to remain within their specific thermal neutral zone are impressive.

The term thermal neutral zone describes the ambient temperature range at which the body needs to make no additional physiological effort to warm or cool itself. Humans have a thermal neutral zone of roughly 18-30°C and Ricky explains that “in other words, in this zone you could stand naked and still maintain your internal core temperature without too much issue.”

Horses, however, have a much larger thermal neutral zone and so feel the cold much later than humans.

“The average adult horse can quite happily live unrugged in temperatures down to 5°C,” says Ricky. “Having visited Iceland, I can testify that the native Icelandic horses live quite happily without rugs in temperatures down to -15°C, with wind and snow blowing horizontally.

“These horses have incredibly thick coats that demonstrate piloerection (the ability of individual hairs to trap warm pockets of air). They are also well acclimatised to their environment.”

While it’s extremely unlikely your horse has adapted to this particular climate, you can be sure your horse is not feeling the cold until much later than you are.

How horses balance their temperature

“A horse’s internal core temperature is a balance between heat generated and lost,” Ricky explains. “Internal body temperature is maintained by metabolic functions, such as digestion, movement and cardiovascular activity. The body also tries to conserve heat through the insulating properties of hair, muscle, fat and skin. A full winter coat is not only insulating, but also provides a degree of water resistance.”

Horses can lose heat in four ways – evaporation, radiation, conduction and convection.

Evaporation

This heat loss mainly occurs from water on the skin, through sweating or getting wet, which is why hosing down after exercise in the summer is so effective.

“Although horses do not pant like dogs, for example, respiration can also play a large role in heat loss,” Ricky adds.

Radiation

This is the normal process of heat moving away from the body without physical contact, such as heat lost from the skin to the environment.

“It is closely linked to the ambient air temperature and body mass,” says Ricky, who gives the example of two breeds that have adapted to very different climates. “An Arabian horse has a higher body surface to mass ratio than a Norwegian Fjord, for example, so will cool more readily in hot temperatures.”

A variation of this is radiant heat loss, when heat is transferred to solid surroundings.

“Keeping a horse in a walled stable in cold weather can actually increase the amount of radiant heat loss” he advises.

Convection

This is caused by airflow across the body – for example, an unrugged horse standing in an exposed field without shelter when the wind chill factor is high will lose heat fast.

Conduction

This is heat loss with direct physical contact.

“Water is a fantastic heat conductor, so wetting of the skin can, once again, increase heat loss. A recent study suggested that horseshoes might also make a difference: hind hooves had significantly lower temperatures when shod,” Ricky adds.

How to tell if a horse is cold

Monitoring your horse’s temperature is good practice. The reading should be between 37.5-38.5°C, but it is important to know what is normal for your individual horse.

“Checking the rectal temperature with a thermometer is the best way,” Ricky advises. “The practice of feeling a horse’s ears to check if he is warm is a very poor indicator of temperature regulation. Placing a hand on his shoulder or trunk will offer some indication if he is too warm and sweaty under his rugs.”

When to rug a horse

So what does this all mean when it comes to selecting winter layers?

“In essence, think twice before grabbing any rug,” says Ricky. “A horse in good body condition, who has a full coat, access to forage, free-roaming exercise and some form of shelter from the elements does not necessarily need more protection.

“If he is young, old, likely to get excessively wet for long periods or exposed to harsh weather conditions, however, he may require extra layers.

“I would actively encourage people to refrain from rugging excessively unless temperatures consistently drop below 5°C, although clipped horses or warmblood breeds may also need light rugs if they are consistently wet or outside their thermo neutral zone.”

Where possible, a horse will avoid conditions that are uncomfortable or increase heat loss – for example, they’ll access shelter when they need it.

“Monitor your horse closely for any subtle changes in behaviour and adapt your management accordingly,” Ricky advises. “But allow him to be a horse and to benefit from a natural cycle of weight gain and loss over the seasons.”

Factors that affect when horses feel the cold

A variety of factors affect how horses horses manage and regulate their temperature, which in turn affect at what a horse will feel the cold.

Breed

Some breeds, including British native breeds, are better adapted to colder climates.

“A study revealed that surface heat loss was seen more in warmblood horses than cold-blooded types, although it was not known whether this was due to body composition or as a direct result of hair coat thickness,” Ricky adds.

“When deciding whether to rug, bear in mind that a horse’s hair coat type, length and density will play a large role in his insulating capacity.”

Age

Young horses may not yet have insulating body fat reserves, which could make them prone to heat loss. Youngsters and foals are also more likely to struggle in colder temperatures as their body has to work harder to generate sooner than an adult horse would.

At the other end of the spectrum, studies have found that older horses (26 and over) are more likely to overheat, especially during exercise. This is due to age-related changes in thermoregulation (body’s ability to return to an optimum temperature range). In addition, changes to coat quality and fat distribution will affect their insulating properties in colder temperatures.

Body condition

While an undernourished horse will have decreased muscle and fat mass, with reduced insulating capabilities, but an overweight animal has the opposite problem.

“As less of his ingested energy will be used for heat production, the excess will consequently be converted into fat – perpetuating obesity,” Ricky explains.

Activity level

An immobile horse (stabled, on box rest or kept in a small paddock) will be unable to walk significant distances, which results in reduced metabolic activity and heat production.

Clipping

Exposed areas of skin will mean reduced hair insulation and increased heat loss.

We tend to clip the neck, shoulders and trunk, which is where most surface heat is lost Ricky explains.

“Hence, while clipping works well for exercise, it can be disadvantageous if the environmental conditions result in further heat loss through radiation or evaporation.”

So when considering when or whether to rug your horse, there is a lot to take into account – and it’s wise to remember that just because you’re chilly, it doesn’t mean your horse is feeling the cold just yet.

• For unlimited access to advice on how best to care for your horse, subscribe to the Horse & Hound website

You might also be interested in: