Just found this study from CSU. It's an interesting read.
Here is some information on winter blanketing that may surprise you. This is the result of a multi-year study done by CSU, using state of the art thermal detection equipment. Colorado State University is widely considered to be one of the top three equine veterinary schools in the country: Blanketing horses is one of the worst things that you can do to a horse in the winter. Horses have the ability to loft and lower their coats to 17 different levels, so it's like exchanging 17 different thermal weights of blankets off and on them all day and night, depending on what they need- except that we don't know what they need as well as they do. Their 'self-blanketing' process works a little like 'chill bumps' do in our own skin. That's why long-haired horses may seem fluffier on some days than on others. Only three things make the 'self-blanketing' process not work: blanketing, clipping, and wind. Not even snow or rain stops their own thermostats from doing the job. Also horses are in 'neutral' (meaning not using energy for either heating or cooling) when the air around them is between 26 and 38 degrees. Otherwise, they're using energy to control their temps. So- since they're cooling their bodies when the temp is over 38 degrees, they're having to use extra energy to cool themselves when blanketed in temperatures o! ver that. Any time a horsethat is outside and has a long coat is shivering, it's because the horse has opted to shiver to warm itself, instead of using the option of moving. Moving generates a considerable amount of heat for a horse, but they sometimes stand and shiver while napping, etc. It does not mean that they need to be blanketed. However- a horse MUST have a way to get out of the wind in order for their 'self-blanketing' abilities to function fully. It turns out that blanketing is done more for pleasing the human, than to fill a need of the horse. The horse blanket industry has done a great job of making us think that their product is a necessary part of good horse keeping- when it is actually an item that is very seldom needed.
You just have to see your distance...you don't have to like it.