The smallest horse in the world is a miniature horse affected by dwarfism called Thumbelina. She is on record with the Guinness Book of World Records as the World’s Smallest Horse. Dwarfism in horses causes similar traits to those seen in humans affected with the disorder. Thumbelina stands only 43 centimeters at the shoulders and weighs 27 kilograms. According to her owners, she will not be bred and horse registries try not to list them as official breeding stock due to various health problems. As a breed, the Miniature horse is classified into two categories; Category A is for horses that stand 82 centimeters and shorter at the withers, and Category B is for horses who stand 82-91 centimeters at the shoulders.

The miniature horse was originally bred for the Hapsburg royalty and King Louis XIV kept them as exotic pets. When they were brought to the Americas, they were bred with the Hackney Pony and the Pony of the Americas to retain their small stature.

The title of these little animals is in dispute. Technically a pony is defined as being 120 to 140 centimeters, and anything larger is termed a horse, but horses and ponies have different characteristics: ponies have stout legs and long torsos while horses have long legs and proportionately smaller torsos relative to their size. Different names include Midget Pony, Pygmy Horse and Miniature Horse, although some distinct breeds within the category are registered such as the Falabella and the South African Miniature Horse.

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