Einstein, The World's Smallest Miniature Horse

Miniature horses are friendly and interact well with people. For this reason they are often kept as family pets, though they still retain natural horse behavior, including a natural fight or flight instinct, and must be treated like an equine, even if they primarily serve as a companion animal. They are also trained as service animals, akin to assistance dogs for people with disabilities. While miniature horses can be trained to work indoors, they are still real horses and are healthier when allowed to live outdoors (with proper shelter and room to run) when not working with humans.
They are generally quite hardy, often living longer on average than some full-sized horse breeds; the average life span of miniature horses is from 25 to 35 years.