Dapper Dan. Hat a fab name xI used to have an older mare that didn't handle cold well, and she got a blanket when it was cold. If it's a cold rain, I make sure they have hay under the shelter and they can stay there if they want to. But mine are on pasture and can move about, grazing, to stay warmer. One problem could be a bossy horse that won't let another under the shelter. Have to keep an eye on that. I will be keeping an eye on Dapper Dan this winter, as he is 24. But he has thick, pelt-like coat and doesn't seem bothered by cold.
But, no shivering is allowed. Any horse that shivers gets a blanket.