When placed between the shoe and hoof it flexes and pushes the snow from the center of the hoof and shoe. This works well and is inexpensive. WD40 comes in a small spray can that can be easily packed in your bag. Probably the easiest thing to relieve snow build-up is to take the shoe off in the winter. When doing this you must keep in mind the type of hoof your animal has.
Some black hoofs are brittle and break off easily while others are solid.
White hoofs may be soft and not hold up under wet conditions. I've found animals with white hoofs are more tender-footed. There is a product that's on the market called the Easy- Boot. The Easy-Boot was made to place on your horse's hoof if it thows a shoe. This Easy-Boot has evolved into a very useful tool.