Melamine-induced nephrotoxicity in weaned piglets in Serbia

Abstract

Melamine is not approved for use in animal feed, although evidence of melamine poisoning in pigs has been found. Melamine in animal feed can induce nephrolithiasis, chronic kidney inflammation, bladder carcinoma and even death in animals. In September 2011, nine hundred 40-60-day-old piglets from a commercial finishing farm in Serbia developed anorexia, wasting, polydipsia and lethargy. At necropsy, the main macroscopic finding in ten necropsied piglets was observed on the kidneys. The kidneys were slightly enlarged and firm in consistency. The cortical surface was wrinkled, with a diffuse distribution of the yellow foci in the cortex and medulla. Microscopically, these yellow foci were accumulations of crystals located predominantly within the lumina of the dilated distal straight and convoluted tubules and collecting ducts. The crystals appeared variable and birefringent when viewed under polarized light. Two types of crystals were observed: the first type had several dark striations radiating from the eosinophilic round centre, while the second type consisted of pale green to brown irregular striated aggregates without an eosinophilic centre. In all cases, multifocally, there were moderate aggregates of lymphocytes, plasma cells, macrophages and multinucleated giant cells within the interstitium. From the clinical signs, necropsy findings, histochemical and toxicological results, it was concluded that melamine-contaminated feed was the primary cause of nephrotoxicity and death in the observed piglets. To our knowledge, this is the first report of melamine poisoning in pigs in Serbia.