Melanosis Contributing to Downgrading in Processed Broiler Chickens in Argentina: Preliminary Diagnostic Findings

Melanosis is scarcely reported as a potential cause of carcass downgrading in broilers worldwide. We described the preliminary diagnostic findings of dermal and celomic fat tissue melanosis in a total of four episodes of increased downgrading in 31-to-50-day-old male Cobb500TM broiler chicken carcasses at a processing plant in Argentina from November 2016 to March 2022. Veterinary inspectors evaluated and sampled a total of 10 carcasses. Gross findings included the gray discoloration of subcutaneous tissue in wings and legs, celomic fat tissue and peritoneum. Microscopically, melanocytes infiltrated the connective tissue and adipose cells of subcutaneous tissue in the skin of legs and wings as well as the celomic fat tissue of all 10 birds. The Fontana–Masson stain revealed black melanin granules in subcutaneous tissue and celomic fat tissue, demonstrating its value as a histologic tool to confirm grossly compatible melanosis in all of the evaluated tissues sampled at the broiler processing plant. We propose to add melanosis as one of the less frequently and rare diagnosed cutaneous darkening conditions which potentially contributes to downgrading in chicken processing plants globally.