Horse
Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus".
Equid hybrid
From the 20th century equid hybrids were being created., though breeding for mules and hinnies had been going on since ancient times. The first crossbreeding was with zebras and donkeys. Equid hybrids can be traced back to Africa where there are vast amount of equid species which resulted in natural crossing creating hybrid species. These hybrids were found to be more efficient than the original species because they poses certain traits of both species so scientists began to experiment by crossing other species of horse family and categorizing them as Equid Hybrids. Equid hybrids are now bred commercially. Mules bred from mammoth studs and stock or draft mares can be as large as seventeen hands and are as strong as a normal horse. Other mules are bred for pets or for entertainment such as zoo, these are the miniature horses or miniature donkeys.