North American donkeys constitute approximately 0.1% of the worldwide donkey population.^[1][a] Donkeys were first transported from Europe to the New World in the fifteenth century during the Second Voyage of Christopher Columbus,^[2]: 179 and subsequently spread south and west into the lands that would become México.^[3] They first reached (what is now) the United States in the late seventeenth century.^[4]: 11 Donkeys arrived in large numbers in the western United States during the gold rushes of the nineteenth century, highly regarded as pack animals and for working in mines and ore-grinding mills.^[5] From about 1785, some select larger donkeys were imported from Europe to the eastern part of the continent.^[4]: 9

There are no true-breeding North American donkey breeds.^[6] Breed societies in Canada and the United States register donkeys, according to their size, as miniature, standard or mammoth donkeys.^[3][7][8] These are reported as breeds to the Domestic Animal Diversity database, a division of the Food and Agriculture Organization of the United Nations, by the National Animal Germplasm Program (of the Agricultural Research Service of the US Department of Agriculture), as are the burros (Spanish for 'donkey') – a feral population of desert-dwelling donkeys in the southwestern U.S. (mainly Arizona) – and the spotted, a color breed.^[9]

The first asses came to the Americas aboard ships of the second voyage of Christopher Columbus, landing at Hispaniola in 1495.^[2]: 179 In the early days of the conquistadores, jackasses were highly valued as sires for mules,^[10]: 284 which were esteemed as riding animals by the Spanish, and reserved for the nobility.^[11]: 284 Mules were bred for expeditions to mainland America, with males preferred for pack animals and the females for riding. The first shipment of mules, with three jacks and twelve jennies, arrived in México via Cuba ten years after the conquest of the Aztecs in 1521. Mules were used in silver mines, and each Spanish outpost across the empire bred its own mules with its own jack.^[5]

The first presence of donkeys in what is today the U.S. is, sometimes, reported to date from 1679, when a Jesuit priest named Eusebio Kino transported several from Sonora, northern Mexico, to a new mission at San Xavier del Bac, in what is now Arizona;^[12] however, Kino did not arrive in the Americas prior to ca. 1681, likewise he was not in Sonora until 1687.^[4]: 11 Roughly 200 years later, donkeys arrived en masse in the western U.S. during the gold rushes of the nineteenth century, as pack animals and for use in mines and ore-grinding mills. The widespread use of donkeys for work largely came to an end with the collapse of the mining boom, as well as the subsequent introduction of railroads across the nation, especially in the west. With little value, many animals were simply turned-loose, becoming the herds of free-roaming burros that inhabit the deserts and highlands of Arizona today.^[5]

From about 1785, some large donkeys were imported from Europe to the eastern United States, and were used for the production of mules.^[4]: 9 In 1888 the American Breeders Association of Jacks and Jennets started a stud-book for these animals under the name American Mammoth Jack.^[4]: 9 In 1923, this stud book merged with the Standard Jack and Jennet Registry of America, which had been set up in 1908; in 1988, its name was changed to the American Mammoth Jackstock Registry.^{[4]: 9 [13]} Breeds that may have influenced the mammoth include the Maltese, the Baudet du Poitou, the Andalusian, the Majorcan and the Catalan.^[4]

In the twentieth century, donkeys came to be more frequently kept as farm animals, pets or as livestock guardian animals in the U.S., among other nations. In 1929, Robert Green of New York imported seven donkeys belonging to the smaller, indigenous Sardinian breed to the U.S.; the first foal was born that same year. Although never considered miniature in their country of origin, these animals were soon known as "Miniature" or "Miniature Mediterranean" donkeys. Green was a lifelong advocate, and said of his animals: "Miniature donkeys possess the affectionate nature of a Newfoundland, the resignation of a cow, the durability of a mule, the courage of a tiger, and an intellectual capability only slightly inferior to man's." By 1935, there were 52 of them, and some were sold. Further Sardinian donkeys were imported, as well as similar—but quite distinct—Sicilian animals.^[14] A register of miniature donkeys was formed in 1958, by Bea Langfeld, the first professional breeder of miniature donkeys in the United States; in 1987, it was merged into that of the American Donkey and Mule Society, which was formed in 1967.^[4]: 8

Both the Canadian Donkey and Mule Association and the American Donkey and Mule Society register donkeys according to their size, as miniature, standard or mammoth donkeys.^[3][7][8]

Adult miniature donkeys stand 36 inches (91 cm) or less at the withers.^[3][7][8][b]

Small standard donkeys stand from over 36 to 48 inches (91 to 122 cm) and large standard donkeys stand from over 48 inches (120 cm) to 54 inches (140 cm) for jennies, or 56 inches (140 cm) for jacks and geldings.^[3][7][8]

Mammoth jennies are taller than 54 inches (140 cm), and mammoth jacks and geldings over 56 inches (140 cm).^[3][7][8]

Any donkey with at least two spots behind the throatlatch and above the legs can be registered with the American Council of Spotted Asses under the trademarked name American Spotted Ass.^{[4]: 10 [15]}