Appaloosas are prone to develop equine recurrent uveitis and congenital stationary night blindness; the latter has been linked to the leopard complex.

Images of domesticated horses with leopard spotting patterns appeared in artwork from Ancient Greece and Han dynasty China through the early modern period.

In North America, the Nez Perce people of what today is the United States Pacific Northwest developed the original American breed.

The modern breed maintains bloodlines tracing to the foundation bloodstock of the registry; its partially open stud book allows the addition of some Thoroughbred, American Quarter Horse and Arabian blood.

[3] Because the occasional individual is born with little or no visible spotting pattern, the ApHC allows "regular" registration of horses with mottled skin plus at least one of the other core characteristics.

[1] There is a wide range of body types in the Appaloosa, in part because the leopard complex characteristics are its primary identifying factors, and also because several different horse breeds influenced its development.

Then, 18th-century European bloodlines were added, particularly those of the "pied" horses popular in that period and shipped en masse to the Americas once the color had become unfashionable in Europe.

[6][7] The original Appaloosa tended to have a convex facial profile that resembled that of the warmblood-Jennet crosses first developed in the 16th century during the reign of Charles V.[5][8] The old-type Appaloosa was later modified by the addition of draft horse blood after the 1877 defeat of the Nez Perce, when U.S. Government policy forced the Native Americans to become farmers and provided them with draft horse mares to breed to existing stallions.

The base colors recognized by the Appaloosa Horse Club include bay, black, chestnut, palomino, buckskin, cremello or perlino, roan, gray, dun and grulla.

[23] Three single-nucleotide polymorphisms (SNPs) in the TRPM1 gene have been identified as closely associated with the LP mutation, although the mechanism by which the pattern is produced remains unclear.

[13][20] A commercially available DNA based test is likely to be developed in the near future, which breeders can use to determine if LP is present in horses that do not have visible Appaloosa characteristics.

[6] The Nez Perce people lived in what today is eastern Washington, Oregon, and north central Idaho,[38] where they engaged in agriculture as well as horse breeding.

[46] Peace with the United States dated back to an alliance arranged by Lewis and Clark,[47] but the encroachment of gold miners in the 1860s and settlers in the 1870s put pressure on the Nez Perce.

[49] The Nez Perce who refused to give up their land under the 1863 treaty included a band living in the Wallowa Valley of Oregon, led by Heinmot Tooyalakekt, widely known as Chief Joseph.

[50] Tensions rose, and in May 1877, General Oliver Otis Howard called a council and ordered the non-treaty bands to move to the reservation.

[47] But on that day a small group of warriors staged an attack on nearby white settlers,[48] which led to the Nez Perce War.

[47] After several small battles in Idaho,[47] more than 800 Nez Perce, mostly non-warriors, took 2000 head of various livestock including horses and fled into Montana, then traveled southeast, dipping into Yellowstone National Park.

[48][50] A small number of Nez Perce fighters, probably fewer than 200,[52] successfully held off larger forces of the U.S. Army in several skirmishes, including the two-day Battle of the Big Hole in southwestern Montana.

[54][55] When the U.S. 7th Cavalry accepted the surrender of Chief Joseph and the remaining Nez Perce, they immediately took more than 1,000 of the tribe's horses, sold what they could and shot many of the rest.

But a significant population of horses had been left behind in the Wallowa valley when the Nez Perce began their retreat, and additional animals escaped or were abandoned along the way.

[46] Haines had performed extensive research, traveling with a friend and Appaloosa aficionado named George Hatley, visiting numerous Nez Perce villages, collecting history, and taking photographs.

[76][77] The American Appaloosa Association was founded in 1983 by members opposed to the registration of plain-colored horses, as a result of the color rule controversy.

The only exception to the bloodline requirements is in the case of Appaloosa-colored geldings or spayed mares with unknown pedigrees; owners may apply for "hardship registration" for these non-breeding horses.

The ApHC does not accept horses with draft, pony, Pinto, or Paint breeding, and requires mature Appaloosas to stand, unshod, at least 14 hands (56 inches, 142 cm).

[25] If a horse has excessive white markings not associated with the Appaloosa pattern (such as those characteristic of a pinto) it cannot be registered unless it is verified through DNA testing that both parents have ApHC registration.

"[2] Appaloosas born with visible coat pattern, or mottled skin and at least one other characteristic, are registered with "regular" papers and have full show and breeding privileges.

A horse that meets bloodline requirements but is born without the recognized color pattern and characteristics can still be registered with the ApHC as a "non-characteristic" Appaloosa.

Because such crossbred offspring are not eligible for ApHC registration,[97] their owners have formed breed registries for horses with leopard complex patterns and gaited ability.

[102] Eighty percent of all uveitis cases are found in Appaloosas with physical characteristics including roan or light-colored coat patterns, little pigment around the eyelids and sparse hair in the mane and tail denoting the most at-risk individuals.

Acetazolamide ("Acet") is used for treating horses with the genetic disease hyperkalemic periodic paralysis (HYPP), and prevents affected animals from having seizures.