The comparative toxicity of Isocoma species in calves.

Isocoma pluriflora and Isocoma acradenia are toxic plants that contain the putative toxin tremetone. It is common for I. pluriflora to poison livestock in the southwestern United States. I. acradenia has been suspected of poisoning livestock but its toxicity has not been confirmed by association with clinical poisonings or experimental studies. Jersey calves dosed with I. pluriflora and I. acradenia for nine days developed "trembles" characterized by skeletal muscle degeneration and necrosis and large increases in serum creatine kinase activity. This is the first report of I. acradenia toxicity in an animal model. This study also demonstrates that I. pluriflora remains toxic even though tremetone concentrations in the plant were low due to storage of the plant for over five years. Thus, supporting recent research which indicates that another toxin in the plant may be responsible for, or at least contributes to causing "trembles" in livestock.