Updated: Nov 4, 2020
Winter is coming and so does the winter fur! But there's more than a thick layer of hair that keep horses warm. Learn about how horses thermoregulate naturally and why we are not necessarily doing equines a favor by rugging them when it's cold.
Horses have various functions for cooling down or keeping warm, to remain a body temperature of 37,5 °C or 100° F. This is called thermoregulation. The horse has fur, skin, body fat, arteries, and sweat glands to help them keep a steady temperature. Let's start with the fur.
Horse’s fur comes in two varieties: summer and winter. This process is mainly regulated by light, through the hormone melatonin. Up North, where I live, horses begin growing their winter coats as early as September. As the days get shorter, the reduction in sunlight triggers the horse's body to increase the production of melatonin, which prompts hair growth. The reverse happens in spring: When days get longer, melatonin production slows and the coat sheds out. If temperature was the trigger for winter fur growth, horses wouldn't begin to grow their coats until it was already cold, and it would come too late to keep warm.
Horse’s natural fur, when not washed with soap, will have some fat in it, making the fur water repellent. Furthermore, the hair on your horse’s body has muscle fibers at the roots that can raise, lower and turn the hairs at different angles. In this way, horsefur changes the insulating ability and varies the airflow on the skin surface.
Skin and body fat
The skin acts as an insulating layer through its relative thickness, and so does the horse’s body fat. Horses tend to gain weight in fall, to store fat in preparation for winter. This makes it hard to slim down a fat horse in fall, just as it's hard to fatten a thin horse in spring. This is due to the horse’s inbuilt ability to gain weight in fall in preparation for winter. Whereas storing body fat in spring, when the warm summer months are just around the corner, is not necessary.
Arteries in the skin itself can contract or expand as needed by means of muscle strength. Contraction prevents body heat loss, as it reduces the amount of blood that is transported to the surface. Expansion allows greater amounts of blood, to flow to the surface and cool the skin down. Sweating also help horses cool down.
Eating forage and drinking lukewarm water
By eating forage (hay and straw), horses also stay warm when it’s cold. Pellets do not have this effect. The reason for this is that natural forage affects the energy turnover of the horse's muscles, similar to physical exercise. (Lindberg SLU)
Drinking cold water will cool down the horse. From my experience, horses drink more in winter when the water is lukewarm, as opposed to cold. This is easily achieved by using a thermo bar or other installation that heats the water. This also prevents horses from getting colic, because the main reason for horses getting colic in winter is because they are not drinking enough water.
How to ruin a horse’s ability to thermoregulate
Three of the mechanisms that horses use to thermoregulate, — their hair muscles, arteries, and sweat glands, — are driven by muscular activity. The main condition for these to function optimally is exercise.
Horses kept in rugs or enclosed in stables, experience an environment where the temperature is almost constant. Such horses largely lack the stimulus of temperature variations to initiate the horse's own heat- regulating mechanisms. These horses do not have the need or ability to use the muscles that are responsible for raising or lowering the hair layer, expanding or contracting arteries in the skin surface, or activating the sweat glands. In the case of persistent lack of use muscles will decrease, until they cannot take care of the function originally intended to do.
Does horses want blankets or not?
A Norwegian study where horses were taught to tell if they wanted rugs or not, showed that horses wanted rugs to a lesser extent than what their owners practiced. The study concluded:
“Horse owners exaggerate the use of rugs on their horses. Horses have the ability to cope with Nordic winter weather with great temperature differences.”
What I think the experiment somewhat failed to consider is that the horses in the study, were already used to wearing rugs, which affects their ability to naturally thermo-regulate. On the other hand, it's impossible to teach horses to tell if they want rugs or not, without using rugs in the first place. Other factors such as forage availability, if the horse has been washed with soap, amount of body fat, light regulation etc., will also influence the horse’s ability to thermoregulate. The bottom line is that this very interesting experiment, showed clearly that even horses who are used to rugs, don`t want to wear rugs as much as their owners want them to.
How I rug my horses
This winter, I'm sticking to the coat that came with the horse. The coat comes in two models: summer and winter. The horse can wear them both indoors and outdoors, in mild weather and in cold. It regulates temperature according to the weather. If it`s cold outside, it will fill itself with insulating air. It`s water repellent and keeps the horse dry during rain or snow. The fur is breathable and dries itself, has a perfect fit and does not chafe. It's incredibly durable and if something happens, it will repair itself.
It`s several years since I stopped using rugs and the horses have never been healthier. The only problem is that some horses get too hot when ridden in winter, due to their thick fur. I have sometimes solved this by shaving off a stripe of fur on their neck. The shaved stripe is enough for them to get rid of excess heat, but there's still enough fur to keep them warm without blankets.
When warm after a winter ride, I let my horses out in fresh air to cool off and dry up. To put a warm horse in a hot, humid stable, with little air flow and maybe even add a blanket on top, is actually not a great idea. Horses love to roll in the cold snow after a ride and then find a place with good airflow to dry the fur. Where's warm humid air makes the fur collapse and it`s not very healthy to breathe in either.
I don't think the occasional use of blankets ruins a horse’s thermoregulation. But if we feel the need to routinely rug a foal or use blankets daily on our riding horse, we should also be aware that we are reducing the horse`s own ability to thermoregulate. Be prepared to take over the responsibility for the horse`s body temperature and make sure to be at hand with suited rugs for any weather change. My experience is that we come a long way with the coat that came with the horse.
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