Crofton weed (Eupatorium adenophorum) toxicity in horses.

The clinical signs and pathology of 6 field cases of a respiratory disease of horses which occurs in the coastal hinterland of south-eastern Queensland are described. The condition has occurred for many years and has been thought to have been associated with ingestion of Crofton weed (Eupatorium adenophorum). Coughing, rapid heaving respiration, decreased exercise tolerance and loss of condition were seen in affected horses. In longstanding cases fibrosis, alveolar lining cell proliferation, oedema, neutrophil infiltration and abscessation were seen. In some cases vascular thrombosis and infarction occur in the lungs. Similar signs and lesions occurred in one horse fed E. adenophorum for 8 months and early lesions in another fed the flowering stage of the plant for about 6 weeks. Lesions also developed in 2 rabbits experimentally fed the plant, but not in sheep or rats.