The short answer might very well be "to blanket." However, for many horses blanketed during cooler months, that extra layer provides more comfort to their caregivers than to the animals themselves. Horses have evolved to have an excellent built-in temperature control: a very thick winter hair coat. Horses require between 10 and 21 days to acclimatize to colder temperatures. For instance, on the first day of 35º F weather, the horse might feel cold, but over 10 to 21 days of similar cold weather, he will "get used to it" and be more comfortable.

If temperatures drop suddenly, you will notice behavior changes, including increased use of shelters if available, huddling together in groups with other horses, and turning their hindquarters into the prevailing wind. These are all activities that help conserve heat. The shivering response will also occur in very cold horses, which generates a pretty substantial amount of body heat, helping to warm internal organs.

Studies in Canada found that for adult horses in cold climates, the lower critical temperature, or the lowest temperature they can tolerate prior to a drop in body temperature, is approximately 5º F, provided they are well-nourished. Given time, any horse can adapt to this low temperature. For temperatures lower than that, they will quickly lose body heat and need our help in order to deal with the cold. We can help either by providing shelter, extra forage, blankets, or a combination of all of the above. Shelter alone can reduce heat loss by up to 20% through protection from wind and rain!

During cold weather, the horse’s hair stands on end, which creates an airspace around the horse where it can trap heat, enabling it to stay warm. This insulation will break down when rain or wind are added to the equation-the former causing the hair to lie flat and the latter blowing away the warm air trapped in the upstanding hair. This phenomenon can also happen when a horse is inappropriately blanketed. In other words, when a blanket with inadequate insulation is put on a horse during milder weather, it forces the hairs to lie flat, taking away the horse’s natural insulation