More than 80% of grey horses will have at least one melanoma during their lives. Horses can develop melanoma at any age – some can even be present at birth! As melanomas are very common in grey horses, many people think they must be benign, incidental skin tumours.
Melanomas are common in aging gray horses, with an incidence of 80% in gray horses older than 15 years old. Common areas for the development of melanomas include under the tail, around the genitalia, in the parotid gland region, on the lips and eyelids.
Although there is no way to prevent melanoma occurrence, increased surveillance, diagnosis, and treatment could reduce the number of horses that develop non treatable lesions.
In nature, light grey, or albino (termed 'white' further on in this work) ungulates (e.g. horses) are rare because of their great vulnerability. They have a higher sensitivity to solar radiation often leading to malign skin cancer and deficiency of the visual system (Pielberg et al. 2008).
Inherited genetics may be a factor of cancer development as researchers have reported a mutation in the STX17 (syntaxin-17) gene that's linked to melanoma incidence in grey horses. Melanomas developing in non-grey horses are generally uncommon but are still possible.
Melanoma is a very common nodular skin disease of older grey horses (usually over 7-8 years of age). More than 80% of grey horses will have at least one melanoma during their lives. Horses can develop melanoma at any age – some can even be present at birth!
Locoregional control of melanoma masses depends on surgical removal and/or intralesional chemotherapy (possibly with adjunctive hyperthermia or electroporation). Systemic treatment is not evidence based but immunomodulators (cimetidine, levamisole) and vaccines can be tried.
Melanomas are a type of skin tumour that occurs predominantly in grey horses. They appear externally as dark grey/black nodules in the skin although they may also develop internally. The most common sites for them to appear are the head, neck and underside of the tail-dock.
Researchers have tracked both grey coat colour and high melanoma risk to the same mutation on a single gene, which explains why these tumours appear so often in grey horses but so rarely in bay or chestnut Coloured horses.
It is unclear if sunlight exposure is the direct cause of melanomas in horses, however. There may be genetic factors or other environmental stresses at play. All that is known is that grays tend to be at a higher risk, despite the fact that melanin protects the skin from ultraviolet radiation.
It also depends on if the tumor is able to be removed and if it has spread to any lymph nodes or vital organs. Many horses can live for several years with melanomas without having any problems, but it is best to have the melanomas removed when they are small because they are easier to remove.
Gray horses have a high incidence of dermal melanomas that are commonly seen around the tail and head. Over 70% of gray horses older than 15 years will develop melanoma. Gray homozygotes are more likely to develop melanoma than heterozygotes.
Groom your horse daily with currycomb and brush, finishing off with the towel. As you curry, use extra elbow grease (or your vacuum) on any manure, mud or grass stains you find. Especially if his coat is toward the darker end of the “gray” range, that may be enough to get most stains out.
Pigmentation in the hair and skin provides some protection against UV light. So, horses with little or no pigmentation, such as greys, palominos, duns, or cremellos, are more prone to sunburn. Any areas with white hair or pink skin will be sensitive to sunlight.
Grey horses or horses with white markings are the more susceptible. Make sure there is shade in the turnout arena, not all horses will use it but might take advantage of the cooler temperature. Applying sunblock on the sensitive skin parts can also help, as well as protecting them with fly masks.
Melanoma is about 20 times more common in white people than in Black people. The lifetime prevalence of melanoma between races is: 1 in 38 for white people.
Horses are vaccinated at 2 week intervals for a total of 4 doses and then boostered at 6 months and every 6 months thereafter if effective. The goal is a reduction in the size of smaller melanomas, possible resolution, slowing of tumor growth of larger masses, and possible prevention.
Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depigmentation, gray does not affect skin or eye color. Gray horses may be born any base color, depending on other color genes present.
Regarding the melanomas in your horse's guttural pouch and on his neck, you do have treatment options that can be tried. Metastatic melanoma, however, remains a genuine treatment problem for many horse owners.
Visible signs of precancerous skin
Crustiness or bleeding. Diameter of less than one inch. Discoloration, often appearing brown, pink, gray, red, yellow, or white. Flat or slightly raised.
Color that is uneven: Shades of black, brown, and tan may be present. Areas of white, gray, red, pink, or blue may also be seen. Diameter: There is a change in size, usually an increase. Melanomas can be tiny, but most are larger than the size of a pea (larger than 6 millimeters or about 1/4 inch).
Sarcoids are caused by bovine papilloma virus (BPV). However, it appears that the virus requires genetically susceptible horses in order to cause sarcoids; in other words, not every horse exposed to the virus will develop sarcoids whereas those that are genetically susceptible are likely to keep developing sarcoids.
Vitiligo. Vitiligo is another common skin disease that most often appears in gray horses as well. This condition is considered an autoimmune disease and leads to depigmentation of the skin due to destruction of melanocytes.
Sometimes, grey horses have spots called dapples. Their manes ranging in color from pale white to slate black. Usually, the mane is a shade or two darker than a grey horse's body coat.