Especially during wet weather the hooves need to be checked and cleaned on a regular basis.
The pastures are pretty muddy after all the rain we had, and some that stuff is really sticky.
Then there are the rocks, and sticks, and who knows what that can get stuck in(on,under?) the hooves.
That is besides the regular trimmings of course (and shoeing for the ones with shoes).
Horses need a lot more roughage in the winter. If you have standing grass for them they can get a lot of that from grazing, but once the grass is gone they need hay, in addition to regular feeds.
The more exposed to weather the horses are, the more hay they need to stay warm.
The horses on our farms all have shelters where they can get in out of the rain, and the wind, so they don’t need as much hay as they would otherwise.
If your horses are out in the weather they will need more hay to keep warm, and the colder it gets they more hay they need to eat.