Gray (Complete)

Description

Gray is a dominant modifier responsible for the gradual, progressive de-pigmentation (fading) of the coat. Gray is not a base color or a dilution, but a gene that slowly removes pigment from the hair. It acts on any base color, whatever the horse’s underlying genotype, which makes it the strongest of all coat modifiers. The fading process may take years, but once hair is de-pigmented the horse’s original coloring never returns.

Because gray is dominant, it is always expressed if present. The final appearance varies from horse to horse: some fade to almost pure white, while others become “flea-bitten” — gray with small non-faded flecks of the original color. Gray horses may also lose pigment in the skin itself, and partially faded skin often shows mottling.

This test reports zygosity: whether the horse carries one copy of the gray mutation or two. If you only need to know whether a horse carries gray at all, our Gray (Presence) test answers that question without distinguishing G/G from G/g.

Melanomas

Equine melanomas occur most often in gray horses. Surveys of aging gray populations have reported melanocytic tumors in roughly 75–80% of horses over 15 years of age, and the same regulatory duplication that causes graying is also responsible for this predisposition. In affected skin, pigment-producing cells are over-stimulated and proliferate beyond what is needed, which can progress to tumor growth.

Most melanomas found in horses are benign. Once present, these are not aggressive in their growth and may progress slowly over several years, typically requiring little treatment. Melanoma is one of the most common skin tumors seen in horses and ponies.

Malignant melanomas can cause severe problems and may be life-threatening. Difficulties arise when melanomas develop internally, or when they grow large enough to ulcerate, bleed and become infected. Large tumors can cause severe weight loss or colic. A melanoma sited where a bridle, saddle, head collar or rug rubs will be uncomfortable and may cause behavioral problems as well as local infection.

Why test for gray

For breeders who specifically want gray foals, a homozygous gray horse (G/G) is ideal. It carries two copies of the mutation and passes gray to every foal, guaranteeing gray progeny. A heterozygous horse (G/g) carries one copy and passes it to roughly 50% of its foals rather than all of them.

Breeders looking to move away from gray need the opposite information. Some breeds carry a high proportion of gray stock, and gray masks whatever base color and dilutions lie beneath it — so a gray horse’s true color genotype is invisible until the gray is bred out or tested for directly.

Because de-pigmentation is slow, it is often not visually apparent whether a newborn foal will eventually gray, and the process can take several years to declare itself. Where a foal has one or more gray parents, DNA testing settles the question immediately rather than waiting for the fade to appear.

Possible Results

Breeds Affected

All horse breeds. Gray is especially common in Arabians, Andalusians and Lusitanos, Lipizzaners, Percherons, Camargue horses, Welsh ponies and Thoroughbreds, but the mutation occurs in any breed.

Reference

A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse.

The study of cutaneous melanomas in Camargue-type gray-skinned horses (2): epidemiological survey.

Related Tests

• Gray(Presence)
• Red/Black Factor (Extension)
• Agouti

Gray masks whatever color lies underneath it. Our Color Panel runs gray alongside our full set of equine color and dilution tests in a single submission, so you can see the horse’s true color genotype.