Many horses appear white, but their underlying genetic mechanisms vary significantly. Most are not genetically white. Distinguishing these differences relies on understanding specific genetic traits and their visible expressions.
Understanding Grey Horses
The vast majority of horses commonly referred to as “white” are grey horses. These horses possess a dominant grey gene (G locus) that causes a progressive lightening of their coat color over time. A grey horse is born with any base coat color, such as black, bay, or chestnut, but white hairs begin to appear, often around the eyes and face, with their first shedding. As the horse matures, these white hairs proliferate, gradually replacing the original pigment until the coat appears entirely white, a process that can take several years. Despite their white hair, grey horses retain dark skin underneath their coat and typically have dark eyes, distinguishing them from truly white horses.
The True White Horse
Horses that are born white and remain white throughout their lives are considerably rare. This true white coloration results from specific genetic mutations, most notably within the “Dominant White” (W locus) genes, which are associated with the KIT gene. These horses are characterized by white hair, but crucially, they also have pink, unpigmented skin and can have brown, blue, or hazel eyes. As of 2021, over 30 variants of the dominant white gene have been identified, each stemming from a spontaneous mutation.
Beyond dominant white, other genetic combinations can produce horses with very light, almost white appearances. These include “double dilute” horses, such as Cremellos and Perlinos. Cremellos result from two copies of the cream dilution gene acting on a chestnut base coat, while Perlinos have two copies of the cream gene acting on a bay or brown base. Double dilutes exhibit pale cream-colored coats, pink skin, and blue eyes, but they are not technically considered true white as their coats still contain some diluted pigment.
Distinguishing White Horse Types
Observing specific physical traits allows for differentiation between grey horses, true white horses, and double dilutes. The most reliable indicator is skin color: grey horses maintain dark, pigmented skin beneath their white coats, whereas true white horses and double dilutes have pink, unpigmented skin. Eye color also provides clues; while grey horses always have dark eyes, true white horses can have dark, blue, or hazel eyes, and double dilutes typically have blue eyes.
Another key distinction lies in their appearance at birth and how their color changes over time. True white horses are born white and remain so, while grey horses are born with a colored coat that progressively lightens. Double dilutes are also born with their light cream coloration, which does not progressively whiten like a grey horse. It is important to note that true albinism, characterized by a complete absence of all pigment and typically red eyes, has not been documented in horses. Horses sometimes referred to as “albino” actually possess pigmented eyes, distinguishing them from true albinos found in other species.