This is kind of obvious, to me, but it dawned on me that in this day and age of, seems like, most people boarding their horses, they may not know this.
A horse's gut is their internal heating element. When they have hay in their gut, it's humming right along and the horse can 'weather' bad weather a lot better than if they don't have much in there.
Now, I've heard both sides of this argument. One side, that I agree with, says that a full gut is good for horsie-warmth and the other side says that it's not so.
From my personal experience, the full gut is the way to go. Not just for warmth for the horse but to keep all systems in check and good running order. In bad, inclement weather, if you keep hay in front of your sweetheart (I mean the horse, not your spouse) you can even do away with using blanket for his protection. If he's in good shape beforehand with enough fat reserves, he will do just fine in cold or cold/wet or wet weather with lots of roughage and plenty of fatty deposits.
If you see your horse is slightly shivering in bad weather, then throw a blanket on for a little bit and throw a lot of hay (roughage) and in no time flat, he'll be right as rain (a play on words there, did you catch that??). Take the blanket off and leave it off after that. That's what I do.
I don't get it when I see thin horses over the top standing out in the cold rain and they look like they dropped in from Ethiopia but there is a nice warm, dry house next to the horse pens. To me, get the owner's ass out there and throw some hay!!
It's all the better if your babykins has a good pasture. He can stand out there all day and night in the ooky rain and come out none the worse for wear. He's had plenty of fuel to stoke the engine and keep him going. He doesn't need to hide behind a barn, his fat is his protection.
Don't remember why some article said that it's not the gut that warms the horse but it didn't make sense to me, not from a practical, personal viewpoint.
Get out there and kiss your horse!!