"Anti-Snowballing When mixtures of snow, ice, mud, manure, grass, or bedding accumulate in the sole area, it can pack densely into large rounded ice mounds that are almost impossible to chip out. The jun ction of the inner edge of the shoe with the sole provides a place for the mud and ice to become securely lodged. Snow will melt from the heat of the sole and freeze onto the metal horseshoe and the snow ball will begin. When a horse is forced to stand or move on the snowballs, he has decreased stability in his fetlock joint. His weight is liable to suddenly roll medially, laterally, forward, or backward. It is extremely fatiguing for his muscles, tendons, and joint ligaments as he constantly must make adjustments to maintain his equilibrium. It is easy for a snowballed horse to momentarily lose his balance and wrench a fetlock.

Applying various substances such as grease to the sole of the barefoot or shod horse or spraying it with a non-stick cooking coating may prevent snow build-up during certain temperatures, but only temporarily. Half-round shoes do a fair job of shedding snow because of the inside rounded edge. However, half-rounds provide poor winter traction so ice nails or borium should be used with them.
Full pads can help prevent snowballing in some situations. The choices include plastic, synthetic rubber, sorbothane, and leather (listed in the order of their ability to resist snow build-up). Full pads with a convex bubble at the sole seem to be only marginally better than full flat pads at popping out accumulated snow. Traction is decreased with full pads."
References :
http://www.horsekeeping.com/hoof_care_and_lameness/winter_shoes.htm