I live in northern Minnesota, and it routinely drops far below -30F, occasionally below -40F, with record lows around -50F. Because horses are NOT native to northern Minnesota, I don't just assume that they can handle it because they are animals, etc. When our temperatures are at their lowest, they get gobs of extra calories in addition to heavy duty blankets, and that is with no work at all. I generally don't ride below 20F above, but if I do, it's an easy trail ride at a walk, or it's in an indoor arena where the wind can't cause a chill. What we need to remember is that even though wild horses can survive in harsh winters, they are not being asked to do anything but search for food and occasionally evade predators. Our horses are asked to work, and also, they are not wild horses. They aren't as hardy, and they require more care. How are they getting water? Eating snow and riverwater can chill their insides. It is alot to think about, but I'm glad you've taken the time to think about it. Alot of people would just pack up and go regardless of temps.