This is a question I ask myself every year as it starts to turn cold. When I got Baron, I was told that he was used to wearing a sheet between 40 and 50 degrees and being blanketed any time the weather got below 40 degrees. I bought him a pretty new sheet which he ripped a huge hole in the first time he wore it. I didn’t buy another one; instead, I blanket him when it gets below 40. Last year I blanketed him as soon as it got anywhere near 40, because I was trying to put weight on him and I know horses burn extra calories when they’re cold. He spent most of the winter under his blanket (and miraculously did not rip it!). He gained weight last winter and I do think being warm helped put the pounds on.
This year I held off on blanketing him in the hopes that he would grow a more substantial winter coat. He gets fuzzy every winter, but not like the other horses in my barn. They turn into veritable wooly mammoths while Baron gets a puny layer of fuzz. I do believe that being blanketed his whole life has resulted in his weak winter coat. If he had grown a puffy layer of fuzz he would have been hot under his blanket. The other horses in my barn have never been blanketed and they have adapted by producing their own blanket of hair. So far Baron doesn’t seem any fuzzier than normal and last night it got down into the 30’s, so out came the blanket.
Here is the annoyance with blanketing: you have to commit to it. A horse stays warm by fluffing his coat out away from his skin to trap heat, and when you put a blanket on, it presses the hair down close to the skin and lessens the heat insulation. Once the blanket goes on and the hair is flattened, you can’t just take the blanket off and send your pony back out to the pasture. His hair has been pressed down and he’ll be cold!