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Grey Coat Colour / Melanoma


Grey is the dominant gene responsible for the gradual and progressive de-pigmentation (fading) of the carrying horse. Grey cannot be considered a base-colour, or a dilution, but rather a gene which slowly removes pigment from the coat. Grey is considered to be the 'strongest' of all coat modifiers, and acts upon any base-colour regardless of the carrying horse's phenotype. The fading process itself may last for years, but once hair is de-pigmented, the horse's original colouring will never return.

Since grey is a dominant gene, where it is present it is expressed. However, the final phenotype of the carrier will vary from horse to horse. Some grey horses fade to full de-pigmentation (almost pure white) whereas others may be 'fleabitten'. Fleabitten refers to grey horses with tiny non-faded spots or 'fleabites.' The grey carrying horse may also experience de-pigmentation of the skin itself, and before skin is fully faded may display 'mottling'.


Equine melanomas occur most often in grey horses, and it is expected that at least 80% of grey horses will develop melanoma. In melanomas from gray horses, both the STX17 and the neighboring NR4A3 gene are over expressed.

Most melanomas found in horses are benign - once present these benign types of melanoma are not aggressive in their growth and may progress over several years requiring little treatment. A melanoma is one of the most common skin tumors seen in a horse or pony.

Malignant melanomas in horses can cause severe problems and can be life-threatening. Problems develop when melanomas are present internally or if they become so large that they ulcerate, bleed and become infected. Equine melanomas sometimes grow so large that they can cause severe weight loss and/or colic. If a melanoma is situated on the head in an area where a bridle, saddle, head collar or rug might rub, it will be uncomfortable for the horse, potentially causing behavioral problems. Infections can also occur.

Genetic Testing of the Grey Gene May Be Beneficial for a Number of Reasons:

Breeding purposes: for those interested in specifically breeding grey foals, Homozygous grey specimens are ideal as they will always transmit the grey gene when bred, thus guaranteeing eventual grey progeny. Those looking to 'breed out' the grey modifier to gain non-fading foals may hope for heterozygous grey horses. Some breed-types have a large percentage of grey stock which through historical lineage may harbour colours and dilutions that are 'hidden' by the masking effect of the grey.

Insight into a foal's potential to fade: since grey may cause slow de-pigmentation, it may not be visually apparent whether or not a newborn foal will eventually fade to grey. The de-pigmentation process may take many years and therefore DNA testing is useful in the cases whereby a foal is born of one or more grey parents and verification of the presence of grey is necessary.

Test Results:

Animal Genetics offers DNA testing for grey factor in horses. The genetic test verifies the presence of the grey mutation and presents results as one of the following:

G/G Grey Positive for dominant grey gene, carrying two inherited copies. Carrier's coat modified and will eventually become de-pigmented. Homozygous grey horses are genetically bound to pass the gene to 100% of their progeny when bred, so all foals will receive grey and fade-out.
G/g Grey Positive for dominant grey gene, carrying a single inherited copy. Carrier's coat modified and will eventually become de-pigmented. Heterozygous grey horses are statistically likely to pass the gene to 50% of their progeny when bred.
g/g Non Grey Negative for grey. Horse will not turn grey.

    Submit a Sample for Testing:

    To submit a sample for testing please click on ORDER and download a sample submission form. Then follow the sample collection and submission instructions.


    Cost per sample is £25. Please see our fee schedules below for bulk and combination rates.

    Equine Fee Schedule English Pounds