Miniature horses, like dogs, can actually be trained to perform a task. They can be legitimate service animals. Dogs and miniature horses are, if I recall correctly, the only two animals protected under the ADA. Most businesses won't risk a lawsuit but businesses ARE allowed to ask what service an animal performs before allowing it on premises. They can't ask what the person's disability is, though. (Think about the intelligence level of the average security guard and you'll realize why most businesses just don't go there.)