Knowing how dirty the ceiling fan can get inside my house, I'd hate to think of how gross one would get over a stall in a dusty barn. I would worry about the dirt gumming up the mechanics in a normal ceiling fan. I prefer the box fans simply because I can move them around to point at the spot where each horse prefers to stand, so I know they are actually getting the most relief. I can also take them down and clean them in the fall before I store them.
"Keep a leg on each side and your mind in the middle"