I was wondering peoples opinions/ experience of winter care for horses - its been a good few years since i?

I live in the upper midwest of the US, so I know cold. All of our horses are outside all of the time without blankets expcept our very old broodmare. She comes in at night. If I am planning on showing during the winter and I don't want a thick haircoat, I put a blanket on. Horses are incredibly adaptable and they have all that hair for a reason.