P37 | The melanosis-melanoma complex in slaughtered equids in the province of Reggio Emilia, Italy

G. Muresu Ibba¹, A. Poeta¹, G. De Lorenzi², G. Pupillo², A. Luppi³, G. D'annunzio³, A. Pezzarossi⁴, I. Bisceglia⁴, L. Mangone⁴ | ¹Az. USL Reggio Emilia, Servizio Sanità Pubblica Veterinaria; ²IZS LER - Sezione Reggio Emilia; ³IZS LER, Sezione Parma; ⁴IRCCS Reggio Emilia, Epidemiology Unit Az. USL Reggio Emilia, Italy

Melanomas are common dermo-epidermal and subcutaneous tumors in horses, especially in gray-coated individuals, representing about 10-15% of all skin tumors diagnosed in this species. The objective of the study was to describe melanomas in slaughtered horses by sex, age, breed, and type of intervention, based on lymph node involvement and distant metastases, in order to provide the inspecting veterinarian with elements to facilitate the diagnosis between melanoma and melanosis. The incidence of this neoplasm increases with aging, but non-sporadic cases have also been reported in young horses. Most of them are initially benign neoplasms, but about two-thirds of them evolve into malignant ones capable of metastasizing. Melanoma manifests as pigmented skin nodules, which can vary in size and shape. These nodules are located in areas of the body with increased pigmentation, such as the head, neck, anus, and genitals. Some horses can develop internal melanomas affecting internal organs like the intestines and kidneys. The study considered 4212 horses slaughtered between January and December 2024 in a recognized establishment located in the Province of Reggio Emilia and inspected by the competent Veterinary Service. Of the 4212 horses, 182 (4.3%) were gray-coated horses destined directly for slaughter from EU countries: France, Hungary, Slovenia, and Poland. Of the 182 gray horses, 28 (15%) developed malignant melanoma. The lesions were sent to the official laboratory of the IZS section of Re for anatomical and pathological examination. Subsequently, the formalin-fixed lesion was sent to the Parma section for histological examination. In 2024, the 28 horses with melanoma (15% of the cases) had an average age of 14.2 years: 8 males (average age 13 years) and 20 females (average age 15 years). Regarding nationality, 21 were French, 2 Hungarian, 2 Italian, 2 Slovenian, and 1 Polish. The topography affected the tail in 26 cases, the heart in 1 case, and the trachea in 1 case. Regarding morphology, 21 were melanomas, 5 were melanocytomas, and 2 were anaplastic melanomas. Regarding the inspection treatment, the neoplasm was removed by trimming in 18 horses, and the entire carcasss was destroyed for 10 horses. Of the 28 cases, 2 had developed lymph node metastases, 12 had distant metastases, and 14 had localized lesions. Most of the horses (75%) were French, female (72%), and the age of onset is slightly different by sex: 13 years old in males and 15 years old in females. The most affected area was the base of the tail (75%). In conclusion, gray horses have an increased susceptibility to developing malignant melanoma largely due to the presence of the Syntaxin17 gene. It is important to proceed with a careful examination of the animal to diagnose any precancerous lesions. Surveillance of even benign lesions is important for their removal, avoiding the sequence benign lesion-malignant lesion, as is a thorough ante-mortem inspection of animals upon unloading at the slaughterhouse. The study clarified the health behavior and fate of meats, including the actions an inspector veterinarian must take in light of EU Regulation 2019/627. Article 45, letters f and o.