The question of whether true white horses exist is common, and the answer is a qualified “yes.” While horses with a pure white coat are certainly real, the vast majority of equines people refer to as “white” are actually a different color entirely. The confusion stems from the visual similarity between a truly white horse and one that has lightened over time due to a separate genetic mechanism. Understanding the difference requires looking beyond the hair coat to the underlying skin and the specific genes responsible for the coloration.
The Genetic Mechanism of Dominant White
A genuinely white horse is one that is born with a white coat and remains that color throughout its entire life. This coloration is genetically distinct and is caused by a group of mutations known as Dominant White, often symbolized by the W gene. These mutations occur on the KIT gene, which is essential for the development of pigment-producing cells called melanocytes.
The W gene mutations prevent melanocytes from migrating to the hair follicles and skin during the horse’s embryonic development. This lack of pigment cells results in an unpigmented, white hair coat and light, pink skin across the entire body. True white horses are relatively rare in the equine population, though they appear sporadically across many breeds.
The eyes of a Dominant White horse are typically dark brown, but some specific W alleles can result in blue or hazel eyes. A simple visual inspection of the pink skin beneath the white hair is the clearest way to identify a true white horse, distinguishing it from other light-colored horses. Because the W gene is dominant, a horse needs only one copy of the mutation to display the white coat, though some forms are thought to be non-viable if two copies are inherited.
Gray Horses: The Most Common “White” Horse
Most horses that appear white to the casual observer are actually genetically designated as gray. This color is controlled by the Gray gene (G gene), a dominant modifier located on the STX17 gene. This gene does not produce a white horse from birth but instead causes a progressive loss of color in the hair over time.
Gray foals are born the color determined by their base coat, such as black, bay, or chestnut, with white hairs beginning to appear shortly after birth. The depigmentation process starts with white hairs intermingling with the colored ones, often first noticeable around the eyes and muzzle. This gradual process means that a horse can transition through several stages before achieving a fully white appearance, which may take many years.
One common stage is the dapple gray, where lighter, circular patches appear against a darker background as the coat lightens unevenly. Later, some horses develop a fleabitten gray pattern, which features small, persistent specks of the original base color scattered across the otherwise white coat. The rate of graying is highly variable, with some horses achieving a pure white coat by six to eight years of age, while others take longer.
The primary difference between a gray horse and a true white horse is the skin color. The Gray gene affects only the hair follicles, not the melanocytes in the skin. Gray horses retain their dark, pigmented skin, typically black or slate gray. This dark skin provides a clear identifier even when the coat is completely white and helps protect them from sunburn.
Why True Albinism Does Not Exist in Horses
The term “albino” is frequently, yet incorrectly, used to describe horses with an all-white coat. True albinism is a genetic condition resulting from the complete absence of the enzyme tyrosinase, which is necessary for the production of melanin. This total lack of pigment would result in a white coat, unpigmented pink skin, and, most distinctively, red or pink eyes due to the visibility of the blood vessels.
No documented case of a horse with true albinism has ever been scientifically confirmed, suggesting that the specific gene pathway required for this condition either does not occur or is lethal in horses. The white horses that do exist, even those with pink skin, all have some pigment in their eyes, which are typically blue, hazel, or brown, not red. This presence of pigment is the definitive counter-indicator of true albinism.
Horses that are mistakenly called “albino” are usually double dilute colors, such as Cremello or Perlino. These colors are produced by two copies of the cream dilution gene on the SLC45A2 gene. This gene acts to significantly reduce, but not eliminate, pigment, resulting in a pale cream or ivory coat, light pink skin, and pale blue eyes. Since some pigment remains, these horses are genetically distinct from a true albino.