BY LIESBETH HAEGEMAN MVM / EQUINE SURGEON AT EQUITOM
PHOTOGRAPHY: COURTESY EQUITOM

“It’s only a melanoma – grey horses always get them.” If you’ve ever heard this at the stable, you’re certainly not alone. Many horse owners believe that melanomas are simply part of owning a grey horse and that there’s no reason to worry. Unfortunately, this common belief is not always true.

While melanomas are often benign, they can still cause serious problems for your horse. In some cases, they can even become life-threatening if left untreated. Knowing what to look for and when to call your veterinarian can make a huge difference

What exactly is a melanoma?

A melanoma is a tumour that develops from melanocytes, the cells responsible for producing pigment. These cells give colour to your horse’s skin and hair. When melanocytes start growing abnormally, they form dark, usually black, lumps called melanomas. These tumours are one of the most common types of tumours found in horses, making up almost one-third of all equine tumours. Although melanomas can occasionally appear in horses of other colours, they are seen almost exclusively in grey horses.

Why are grey horses so prone to melanomas?

The high incidence of melanomas in grey horses is no coincidence. It is linked to the same genetic mutation that gives grey horses their unique coat colour. Unlike horses that are born white, grey horses are actually born their original colour – such as black, bay, or chestnut. During the first years of life, the grey gene gradually causes their coat to lose pigment, so they become increasingly grey before eventually appearing almost completely white. Unfortunately, this same genetic mutation also affects the pigment-producing cells (melanocytes), making grey horses much more likely to develop melanomas as they age. The horse's sex and exposure to sunlight do not seem to influence the development of these tumours.

Where do melanomas usually appear?

Melanomas often develop slowly, which means owners may not notice them immediately. The most common locations include:
• Around the anus
• Under the tail at the tail base
• Around the salivary glands
• The eyelids
• The genital region
• The lips
Although less com-mon, melanomas can also develop inside the body. Veterinarians have found them in the lungs, dia-phragm, spleen, spine, brain and even inside the eye.
Most melanomas are benign when first diag-nosed, but studies suggest that up to 30% may eventually become malig-nant, meaning they can spread to other parts of the body or show a more aggressive behaviour.

Small lump today… big problem tomorrow?

One of the biggest mistakes horse owners make is ignoring a small melanoma because it doesn't seem to bother the horse. The problem is that melanomas usually continue to grow. While this growth is often slow, larger tumours become much more difficult to remove surgically and are more likely to cause complications. melan-omas around the anus can eventually inter-fere with normal defec-ation. The horse may experience discom-fort, swelling, inflam-mation, and constipa-tion. In severe cases, the horse may no longer be able to pass manure, creating a life-threatening emerg-ency. Melanomas under the tail can become so large that part of the tail may eventually need to be amputated.
When melanomas develop near the salivary glands in the neck, they can press against the windpipe and cause breathing difficulties. These examples show why “benign” certainly does not mean “harmless.”...

<a href="https://breedingnews.com/current-issue-2/" target="_blank" rel="noopener">CLICK HERE TO READ THE COMPLETE ARTICLE IN THE ONLINE EDITION OF BREEDING NEWS</a>