Melanoma is the most common tumour in grey horses, affecting the vast majority as they age. Understanding the condition and its welfare implications helps owners make informed management decisions throughout their horse's life.
The welfare challenge of equine melanoma lies in its near-universality in grey horses, its long asymptomatic phase, and the unpredictability of malignant transformation. Most grey horses live comfortably with melanomas for years, but owners must maintain vigilance for signs that previously stable masses are changing — because malignant transformation can occur after a long stable period. The welfare harms of advanced melanoma are significant: large ulcerating perianal masses cause pain with every defecation; compressive melanomas in the parotid region cause dysphagia and respiratory compromise; and metastatic disease causes progressive systemic decline. Early intervention for lesions in high-consequence locations — before they reach sizes that compromise function — represents better welfare practice than waiting until obstruction or pain forces action. Honest discussion between owner and veterinarian about when quality of life is being significantly impacted by melanoma burden, and proactive end-of-life planning, is important for horses with significant disease.