Pyrrolizidine alkaloid poisoning of yaks (Bos grunniens) and confirmation by recovery of pyrrolic metabolites from formalin-fixed liver tissue.

Severe losses of yaks (Bos grunniens) were investigated in the most eastern region of Bhutan. The most serious disease was a fatal chronic skin disease with emaciation and anaemia. Post mortem examinations revealed major lesions in the liver, consisting of hepatic megalocytosis, bile duct proliferation, fibrosis and remodelling of the hepatic structure. There was also renal megalocytosis, ascites and mild to moderate icterus. Pyrrolizidine alkaloid poisoning was diagnosed and confirmed by demonstrating sulphur-bound pyrrolic metabolites of the alkaloids in preserved liver tissue. Skin lesions with hyaline parakeratosis were an important feature. Similar lesions were found in the mucosa of the oral cavity. No records could be found of such skin lesions in any other species or disease. Pyrrolizidine alkaloid poisoning seriously affects the livelihood of the local population which depends almost entirely on the yak. Various control measures are discussed. The key to be found is the identification of the toxic plants.