As we move into late autumn, the colder weather has most of us reaching for our jackets when we go to see our horses. But does this mean it’s time to start rugging up?

We should not necessarily judge what “clothing” our horses need based on how we feel. The horse has a fur coat, of course, and, due to his size, will not lose body heat as rapidly as we do.

Horses are incredibly adaptable when it comes to climate and are found in some of the hottest and coldest places on earth. As they are warm-blooded mammals, a horse will naturally keep his core temperature as close to 38°C as possible — a process called thermoregulation. His bodily extremities may fall as low as 5-10°C in very cold climates, however, or reach as high as 60°C if he is standing on hot sand, for example.

Thermoregulation allows the horse to remain active all year round in a range of climates without the need to hibernate, but in winter he must take in more energy to generate the heat to keep his body at the optimal temperature.

The fuel for this comes from energy stored in the food the horse eats. Heat is generated by breakdown of the foods either inside the cells of the body or by fermentation of fibre within the hindgut.

2 grazing to draw on4

How cold is he?

In simple terms, a horse will feel cold when the air temperature falls below 0°C and hot when it rises above 25°C. This is his thermoneutral zone — within this range he can control his body temperature by simply opening and closing blood vessels in the skin to lose or retain heat “carried” in the blood.

Humans, when naked, have a much higher and narrower thermoneutral zone of 25-30°C. So when we feel cold, our horses will still feel comfortable.

When the temperature drops below 0°C the horse needs to generate heat, via an increased metabolic rate (in effect turning up the central heating and using more fuel). He will also seek shelter and his blood flow will decrease to let the temperature of his limbs drop.

Body temperature is a balance between heat produced and lost. In the cold, the horse loses heat more rapidly and must increase heat production and/or decrease heat loss to maintain body temperature.

Various factors determine how much heat is lost and how much energy a horse needs to use to keep warm.

Weather: the colder the temperature of the air, the bigger the difference between the horse’s surface (skin or coat) temperature and the air — and the more quickly heat will move from hot to cold. Wind causes even faster heat loss due to the wind-chill factor, while rain will make it feel even colder.

We may gain some heat from the sun, even in winter, but the coldest conditions are low air temperature, strong winds and rain.

Size: some breeds cope better with cold than others, but, in general, larger horses retain heat better than smaller ones. Rounder or more compact cob-types have an advantage over finer breeds such as Arabs.

Age: young horses are smaller, often with less body fat, and lose heat more rapidly in the cold. Older horses have a reduced ability to control their body temperature and possibly less body fat, decreased digestive efficiency and other health problems that can contribute to them being more at risk in cold weather.

Diet: heat production is greater on high-fibre diets than high-starch and/or high oil-based diets. Increased addition of energy to the diet is only really necessary when the average temperature drops below 0°C for several weeks, or for younger or older animals or those in poor condition.

Coat: a horse’s coat keeps him warm by trapping air between the hairs. When the coat is wet the hairs collapse and less air is trapped, leading to faster heat loss.

The thickness of a horse’s winter coat, and whether he has yet grown one or has been clipped, will have a big effect on his ability to retain heat.

It has always been thought that changes from a summer to winter coat occur as a result of both day length and temperature. A recent study in Poland, however, found evidence that air temperature rather than daylight appeared to have the strongest influence on the development of the winter coat.

Shelter: studies have shown that mature horses can maintain good body condition — even in severely cold weather — if provided with unlimited good-quality forage and shelter.

One interesting consideration to bear in mind is that a stone shelter or stable will “draw” heat from a horse by a process known as radiation. In the same way that the sun radiates heat to the earth, in the stable the horse becomes the equivalent of the sun and radiates (loses) heat to colder surfaces. So, while he may not need a rug in a wooden stable, he may benefit from one in a building made of stone.

Horses keep warmer when on high fibre diets

Horses keep warmer when on high fibre diets

The healthy way

In addition to radiation, a horse loses heat to his surroundings from his skin surface, through breath, faeces and urine, and through contact with colder surfaces such as the ground.

Before reaching for more rugs, however, it’s worth considering a few important points.

Rugs can rub, especially if they are causing the horse to sweat. Sweating makes the skin hyper-hydrated (the effect we humans get after too long in the bath) and more prone to damage and infection.

While sunlight can penetrate a horse’s coat to generate vitamin D, it cannot pass through winter rugs (or stabling). Vitamin D is involved in the regulation of calcium and phosphorus in bone, so deficiency can lead to decreased bone strength.

Finally, a horse uses a considerable amount of energy to keep warm. If he is too heavily rugged, excess energy will be deposited as fat and can lead to weight gain.

As tempting as it is to rug your horse based on how cold you’re feeling, only by considering the full range of factors will you maximise his health and comfort.

Ref: Horse & Hound; 22 October 2015