A horse commonly perceived as "white" is technically called a grey horse because its coat color is the result of a genetic process where the hair gradually loses its pigment over time, rather than being born truly white. This unique coloration is not a fixed color at birth but an evolving trait.
The Genetic Explanation
The reason these horses are called grey, even when they appear white, lies in their genetics. A horse inherits a dominant grey gene which causes the hair coat to progressively depigment. This means the horse is not born with a white or even light grey coat. Instead, they are typically born with a much darker, solid base color, which then gradually lightens over the years.
How the Color Changes Over Time
The transformation of a grey horse's coat is a fascinating process that unfolds over several years:
- Born with a Base Color: Foals that will eventually become grey are born with a distinct, non-grey coat. They can be born any color, such as:
- Chestnut
- Black
- Palomino
- Bay
- Any other base coat color
- Gradual Lightening: As the horse matures, the dominant grey gene begins to express itself, causing the hair to gradually lose its color. This process is progressive, meaning the coat gets lighter with age.
- Maturation to Grey: A horse carrying the grey gene will typically show significant changes, often turning dark grey between the ages of six and twelve years old. As they continue to age, the depigmentation advances further, eventually making the coat appear almost entirely white. Despite the appearance, the skin underneath usually remains dark, distinguishing them from truly white horses.
Stages of Greying
The progression of a grey horse's coat can be summarized as follows:
| Age Range | Typical Appearance | Genetic Mechanism |
|---|---|---|
| Birth | Chestnut, Black, Palomino, Bay, etc. | Dominant grey gene is present but not yet actively causing depigmentation. |
| Young Adult | Steel Grey, Dapple Grey, Rose Grey | Gradual loss of pigment begins, often resulting in various shades and patterns. |
| 6–12 Years | Dark Grey, Flea-bitten Grey (if spots develop) | Significant depigmentation occurs, with the coat often becoming uniformly dark grey. |
| Older | Appears White (sometimes "flea-bitten") | Continued depigmentation leads to a nearly or completely white hair coat. |
Therefore, when you see a horse that looks white, it is most accurately described as a "grey" horse because its seemingly white appearance is the final stage of a genetic greying process rather than a true birth-white coloration.
