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Department of Veterinary Sciences

College of Agriculture and Natural Resources

Red Rim Elk Lichen Poisoning

In the Winter of 2004, approximately 600 elk were poisoned and died as a result of eating Xanthoparmelia chlorochroa, a free-living lichen common to many areas in the West.  My group identified the causative agent of the die-off.  The discovery that X. chlorochroa is toxic generated a number of additional questions: “are animals that have eaten lichen safe to eat?”, “what made the lichen toxic in this particular year?”, “how do we know when this will happen again?”, “are other species (cattle, sheep, horses, antelope) affected?”, etc.  My group is working to elucidate the active ingredient of the lichen, an essential first step to answering any of these questions.

This quest has been given emphasis by virtue of the facts that 1) other species of Xanthoparmelia are sold to people as a “herbal Viagra” and for weight loss and 2) we have diagnosed lichen poisoning in domestic animals since the original case, suggesting that it may have been overlooked in the past.  So far we have demonstrated that the lichen is considerably more toxic in mice and sheep that can be accounted for by its usnic acid content and usnic acid per se does not account for the syndrome seen in the field cases.

Investigators: Dr. Merl Raisbeck, Dr. Todd Cornish 


  • R. N. Dailey, D. M. Montgomery, J. T. Ingram, R. S. Siemion, M. Vasquez, M. F. Raisbeck,  (2008):  Toxicity of the lichen secondary metabolite (+)-usnic acid in domestic sheep.  Vet Pathol 45:19–25.

  • R. N. Dailey, D. L. Montgomery, J. T. Ingram, R.Siemion & M. F. Raisbeck (in press 2008):  Tumbleweed shield lichen (Xanthoparmelia chlorochroa) toxicity.  J Vet Diagn Invest

  • W. E. Cook, M. F. Raisbeck, T. E. Cornish, E. S. Williams, B. Brown, G. Hiatt, T. J. Kreeger (2007):  Paresis and death in elk due to lichen intoxication in Wyoming.  J Wildl Dis 43:498-503.

  • W. E. Cook, T. E. Cornish, E. S. Williams, B. Brown, G. Hiatt, T. J. Kreeger and M. F. Raisbeck (2007):  Xanthoparmelia chlorochroa intoxication in wapiti (Cervus canadensis).  pp. 40-45 in Poisonous Plants:  Global Research and Solutions (ed. Panter, K, Wierenga, T and Pfister, J) pub. CABI  Publishing, Wallingford, OX.

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