The comparative toxicity of Isocoma species in calves

Authors: Davis, Thomas - Zane; Green, Benedict - Ben; Stegelmeier, Bryan; Lee, Stephen

Submitted to: Toxicon: X
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2019
Publication Date: 1/2/2020
Citation: Davis, T.Z., Green, B.T., Stegelmeier, B.L., Lee, S.T. 2020. The comparative toxicity of Isocoma species in calves. Toxicon: X. 5. https://doi.org/10.1016/j.toxcx.2019.100022.
DOI: https://doi.org/10.1016/j.toxcx.2019.100022

Interpretive Summary: Isocoma spp. are part of the Asteraceae family and are commonly found growing in riparian zones along river valleys, drainage areas, or dry plains in the southwestern United States and Mexico. Of the 16 Isocoma spp. only I. pluriflora (rayless goldenrod) is widely reported to be toxic. I. acradenia has been suspected of poisoning livestock but research has not confirmed this suspicion. I. pluriflora and I. acradenia both contain tremetone, which has been reported to be the toxin in Isocoma spp. however, purified tremetone has not been definitively demonstrated to be myotoxic in any animal or biologic model. In this report, we were able to produce and describe I. acradenia intoxication in cattle for the first time. Additionally, the lesions and serum biochemical changes produced in the I. acradenia dosed calves was the same as the disease produced in the I. pluriflora dosed calves with a few minor differences in the most affected muscles in the two groups as well as the lesions being more severe in the I. pluriflora treated group. Additional studies with extracts and other plant chemotypes should be conducted to definitively determine the toxin in Isocoma spp. and white snakeroot and to determine the specific mechanism involved in poisoning.

Technical Abstract: 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 creatine kinase activity. This is the first report demonstrating the toxicity of I. acradenia in an animal model. This study also demonstrates that I. pluriflora remains toxic even though tremetone concentrations in the plant were low as they had decreased more than 20-fold since collection. Thus, supporting recent research which indicates that another toxin may be responsible for, or at least plays a role in causing “trembles” in livestock and “milk sickness” in humans.