LOL. I agree^^ That could take FOREVER. Im not sure, but if the horse tried to eat human nailpolish, it may be toxic. I use Twinkle EVERYTHING(x People think Im crazy for making them look like unicorns or something, but its alot of fun. Plus, it makes them look so cute(:
You might want to take out shares in a nail polish company :S
I wouldn't use it, firstly - it would look ridiculous and won't be good for the hoof, plus is toxic and removing it with polish remover, will dry out the hoof wall significantly.
Stick with good old hoof black or oil if planning on showing, and twinkle toes if you really MUST put your horse through that sort of humiliation!