Ice, snow, mud: They're all liable to cause some unforeseen hoof and leg problems. To prevent your horse from slipping, shovel walkways between paddock and barn, and use salt or sand for extra grip. Consider asking your farrier to install borium -a super hard steel-studs on your horse's shoes if you plan to ride outdoors in the wintertime.
To prevent snowballs from building up in his hooves, coat the under side of the hoof with Vaseline. Also, consider asking your farrier to add pads to your winter shoeing routine.
Hard, frozen ground can wreak havoc on your horse's hooves, especially if they are dry. Use hoof dressing liberally during the winter, especially on unshod horses prone to cracking.
Pick out your horse's hooves every day, at least once, even if you are not riding. Snow and frozen mud can cause bruises on his soles.