Melanoma in horses: distribution by sex, age, nationality, and slaughterhouse findings in 28 horses from Northern Italy.

Melanoma tumors are common in grey horses, and this study analyzed their occurrence and characteristics in 28 slaughtered horses from Northern Italy, focusing on factors such as sex, age, nationality, tumor locations, and the implications for meat inspection procedures.

Study Objective and Population

• The research aimed to characterize melanomas in horses slaughtered in Northern Italy by examining the distribution of tumors based on sex, age, and nationality.
• The study also evaluated veterinary inspection findings during slaughterhouse processing, particularly relating to lymph node involvement and metastasis.
• The sample included 182 grey horses examined over one year (January to December 2024), with 28 melanoma cases identified.

Demographics and Melanoma Incidence

• Out of 182 grey horses, 28 were found to have melanomas, representing approximately 15% of the grey horse population examined.
• The average age of affected horses was 14 years, suggesting melanomas are more common in middle-aged to older horses.
• Sex distribution of affected horses: 8 males (mean age 13 years) and 20 females (mean age 15 years), indicating higher prevalence in females in this dataset.
• Nationalities of affected horses were diverse, with the majority being French (21), followed by Hungarian (2), Italian (2), Slovenian (2), and Polish (1).

Locations and Types of Melanomas

• The most frequent tumor locations were:
  • Base of the tail and perineal area (26 cases)
  • Cardiac muscle
  • Trachea
• The tumors were classified histologically as:
  • Dermal melanomas (19 cases)
  • Melanocytomas (5 cases), a usually benign type
  • Anaplastic melanomas (2 cases), a more aggressive form
  • Noncutaneous melanomas (2 cases), located deeper in tissues rather than the skin

Metastasis and Veterinary Inspection Outcomes

• Metastasis analysis showed:
  • 2 horses had lymph node metastases, indicating regional spread.
  • 12 horses had distant metastases, suggesting advanced disease affecting other organs.
  • 14 horses had localized lesions without metastasis.
• Based on disease progression, veterinary inspection interventions included:
  • 18 horses underwent tumor removal with carcass trimming to ensure meat safety.
  • 10 horses had to be completely condemned (carcass not fit for consumption) due to extensive disease or metastasis.

Significance of Findings

• This study highlights the clinical behavior of melanomas in slaughtered horses, particularly in grey horses, which are predisposed to this tumor type.
• Understanding tumor distribution by sex, age, and nationality can help identify risk factors or population trends.
• The findings inform veterinary protocols for postmortem inspection, guiding decisions about carcass trimming or condemnation to ensure public health and meat quality.
• The study underscores the need for awareness about melanoma progression in horses destined for slaughter to manage food safety effectively.