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. 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.
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. The sole retains it's cupped traction feature, can respire normally, and can descend with weight bearing. As the horse's weight descends on the hoof the pads flex and dislodge the snow that accumulates at the junction of the shoe and sole. Tube pads with open shoes work well in most weather conditions.