PH - Paint Horse Association of Australia

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Tesio was correct - grey in horses is not a "colour" or a "factor"
- it is a "disease of the coat".
STORY: ANGELA NEWTON FROM KERRY MORGAN B.A.DIP.ED - OCTOBER 24, 2003 (REVISED NOV 2, 2005)
PERSPECTIVE TWO - (AS DISCUSSED FROM PREVIOUS ARTICLE)...
Does any other animal go grey like a horse goes grey?
There are animals that are grey in colour but they are born
grey, there are shades of grey and agouti among cats, dogs,
rabbits, goats, there are "blue" cows, there are even other
colours in the horse that appear grey, such as blue roan,
and roan associated with Appaloosa colouring. People lose
their hair colour from middle to advanced age. But unique
among animals, horses "go grey".
A grey horse is can be born any colour, and the greying of
the coat begins some time after birth and progresses. Very
aged grey horses are white, with or without a "fleabitten"
effect. Breeders can usually identify a foal that will turn
grey by the presence of grey hairs around the eyes. Only
foals that have at least one grey parent can go grey, but
conversely a foal with 2 grey parents may remain non-grey,
even in breeds with a high percentage of homozygous greys
such as the Lipizzanner.
A grey horse has the usual complement of genes for colour
and/or pattern inherited from both parents, but geneticists
have long regarded the tendency to "grey out" as a factor
that acts in addition to the genotype for coat colour. The
inheritance pattern for grey follows Mendelian rules. It can
be homozygous or heterozygous, and it is dominant in that
if the animal carries one gene for the factor, the horse will
appear grey. A grey horse must have at least one grey
parent, ie the factor cannot be carried recessively.
I believe that the "factor"
that makes a horse go grey
is in fact an inheritable
dominant mutation which
affects the skin and hair of
the grey horse, and which in
its full expression is "grey
horse melanoma".
Gower (1999, p. 60)
states the following:
"Throughout the life of a
grey, pigment is removed
from the hair and
redeposited in the gut or skin, and this is thought to be
responsible for…the slow-growing deposits of pigment
loosely termed ‘melanoma’.
Fintl & Dixon (2001) refer to a 1972 survey by Stannard
which indicated that "more than 80% of grey horses over
15 years old were affected with such [melanotic] growths".
In the same article, Yager et al (1993) is quoted as
suggesting that all grey horses would eventually develop
such lesions if they lived long enough.
Drs Sutton and Coleman from Uni. Qld. studied 97 grey
horses and 16 coloured horses at a pet food abattoir, and
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The Paint Horse Journal
February - March 2007