I thought this was weird too but my understanding is that miniature horses actually make fantastic service animals. That article touches on some of the reasons

I thought this was weird too but my understanding is that miniature horses actually make fantastic service animals. That article touches on some of the reasons, including that they're housebroken, intelligent, capable of leading the blind, can be trained to have a very calm demeanor, are often more patient than dogs, mitigate issues with allergies because they don't shed and they can't get fleas. Also the big one: miniature horses live significantly longer than dogs, reducing the number of times an owner has to re-pair and form a new relationship with a new service animal.