Melanomas affects 80% of grey horses, usually when older, but can start at 4yo and onwards. They are rare in other colours. They are usually benign, with 1 in 1000 are malignant
Pigment tumours , dark spots becoming raised, nodular and large / irregular /interconnected over the years. These are commonly under tail, around anus, sheath, ears, eyes, inside salivary glands / guttural pouches , seen as bulges under skin on head, and upper neck.
When large, melanomas require local management, such as cleaning, fly control, moisturising, surgical management including cryotherapy. Oral crimetidine is expensive but can arrest growth.
Melanomas may lead to faecal incontinence, discomfort and be a reason to euthanise an old grey horse (25 years plus) However normally greys function normally and happily into old age.