Melanomas are extremely common in grey horses and while often benign initially, can cause significant welfare problems as they grow and become internal.
Grey horse melanoma creates a long-term welfare management challenge. Small, stable perianal melanomas in young grey horses may cause no welfare harm for years. However, progressive growth around the tail base can eventually impede defecation, cause painful pressure on surrounding structures, and ulcerate to produce malodorous discharging lesions that are difficult to heal. Parotid melanomas that grow medially can compress the airway or esophagus. Internal metastasis causes organ dysfunction without obvious external signs. Regular monitoring with measurement and photographic documentation allows early identification of progressive lesions that warrant treatment. Surgical excision of small accessible lesions before they become large and locally invasive provides the best welfare outcomes.