As most horse owners are aware, grey horses are more prone to developing melanomas as they have more pigmented skin, and melanoma tumours arise from a mutation in the cells that make up the pigmented skin. Many reports suggest that the chance of a melanoma arising in a grey horse over 15 years old are as high as 80%. Although numerous amounts of research have been done on cancer in horses, it is still unclear why they develop.
It is suggested that these mutations which cause the melanomas are inherited or enhanced due to UV radiation (however most melanomas arise in areas that do not normally get direct sunlight). No matter the circumstances of how they arise, there is currently no proven prevention; however, treatments for melanomas are constantly evolving. It is imperative that early detection and removal is administered in order to keep your horse healthy and safe as well as keeping grey horses constantly rugged to protect them from direct sunlight.
In order to detect cancer before it becomes too late, a thorough physical exam by a vet is required. Normally these melanoma tumours will be external and able to be identified easily, although in some instances there may be signs pointing to internal cancerous tumours that will require further examinations through an ultrasound.
Unlike malignant tumours, the ones in grey horses are normally benign tumours that are not nearly as fatal as they progress at a much slower rate. In saying this, malignant tumours are still able to develop on horses, although they are not as common. Due to this many of these horses do not die from a tumour but due to the effects that it has on other areas of the body as it grows and becomes harder to remove.
A treatment for a tumour will depend on numerous factors including location, size, and effect on daily functions. It also depends on how the vet approaches most tumours – some treat aggressively by removing the lesion instantly as they are easier to remove early on, while other vets prefer to monitor it over time believing that most tumours in horses are benign.
It is important to treat all possible melanoma’s as malignant as it could potentially save your horses life. 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.