Melanoma is extremely common in grey horses and presents unique welfare challenges as tumors slowly progress over years to decades.
Grey horse melanoma creates a long-term welfare management challenge rather than an acute crisis. Most horses live with benign melanomas for many years without significant welfare impact, but the progressive nature of the condition means owners must monitor for signs of malignant transformation including rapid growth, ulceration, and behavioral changes indicating pain. Perianal tumors that grow large enough to impede defecation cause significant chronic discomfort, and internal spread causes the welfare impacts of organ dysfunction including colic, weight loss, and reduced appetite. The gradual progression means welfare decisions including surgical debulking, medical management, or humane retirement must be made repeatedly across the horse lifetime. Owners of grey horses should establish baseline documentation of melanoma locations and sizes from an early age, enabling reliable monitoring of progression over time.