Toxic hepatopathy and photosensitization in cattle fed moldy alfalfa hay.

Cattle in 2 herds developed type-3 photosensitization after eating moldy alfalfa hay. Clinical signs included severe epidermal necrosis of unpigmented skin and marked decrease of milk production (herd 1). One herd had 18% mortality. Values for serum gamma-glutamyltransferase, lactate dehydrogenase, aspartate transaminase, and serum bilirubin were high in affected cows. Biliary epithelial degeneration and necrosis affecting the smaller bile ductules is the most consistent histologic lesion. Biliary hyperplasia, early portal fibroplasia, hepatocellular vacuolar degeneration and necrosis, and cholestasis were commonly seen. Mold growth on the alfalfa hay associated with prolonged wet weather prior to harvest was common to both herds. The cases reported here document hepatoxicosis and photosensitization associated with feeding moldy alfalfa hay grown in southeastern United States.