Horses in Blankets

We are having a cold week, and when nights get in the single digits or low teens, I blanket the horses. Even though they are built for cold, I can't stand to have them bear THAT degree of cold without a little comfort. I'm always trying not to leave the blankets on too long, as I don't want them to start shedding their winter coat, but when the nights stay so cold for so long I begin to wonder how long is to long to blanket. This morning when I left to walk to work it was 18 degrees, and I decided to leave the blankets on for today. It's nice to have some winter weather, but at the same time, I get sick of cold fairly quickly.