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Gray
: new hairs grow in with inhibited pigment, increasing in both number
and lack of pigment as the
horse ages.
G
: the gene that causes graying; a dominant gene,
abbreviated "G".
g : the gene that keeps pigment
constant in each
successive new hair (during shedding); non-gray, or "g".
Dominant and recessive genes are
explained in "Genetics".
There is a test for gray. DNA color test links are on
THIS PAGE.
The gray gene causes depigmentation (loss of pigment) in hair.
The hair grows in with "inhibited" pigment: at first
there may simply be less
pigment than the original, unchanged hairs, or with "distorted"
pigment, sometimes even making areas of a palomino look black. The final hairs are crystal-clear, and when they reflect ambient
light, they appear white.
The skin underneath the
previously-colored hairs stays dark except for in a few cases (see
gray depigmentation, below.)
 Graying often starts before birth, in which case a foal will be
born with gray (white) hairs around its eyes, giving the appearance
of "goggles" (seen here in a foal bred by Simone LaPlante).
Sometimes gray hairs don't start to appear until much later, as late
as age 2, and then sometimes they start appearing first in the tail
(see bottom picture).
In all cases, the horse has more pigment-impaired hairs every
year, until, in advanced cases, they can appear snow white all over. The number of
years this takes to happen can vary greatly. During the
process, otherwise-unexpected changes can happen in other areas of
pigmentation: the legs of palominos turning gray have been
known to turn "black" during the process! (See the
oddly-pigmented legs on the foal, above. Usually red-based
foals are born with legs more of a buff color.)
Most "white horses" seen in pictures and in movies, etc., are
actually highly advanced cases of graying, or lack of pigment of the
hair.
"Gray depigmentation"
Some gray horses also lose the pigment in parts of their skin,
resulting in what is usually called "gray depigmentation", similar
to vitiligo in humans. It's usually found in areas where there
is little or no hair.
Gray may also be spelled "grey", which is a more British
spelling, whereas "gray" is a more American spelling.
 This picture shows a horse that is going gray
beginning with its tail hair. This web master hopes to
investigate whether the way horses turn gray is inherited
separately, implying different genes/mutations causing it.
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