Progress 01/01/05 to 12/31/06
Outputs
Yearling ewes were dosed with (+)-usnic acid in an attempt to replicate X. chlorochroa toxicity in elk. Doses up to 485 mg/kg body weight did not cause clinical signs, biochemical changes or morphologic lesions. Doses greater than 647 mg/kg were lethal within seven days. Intoxicated sheep exhibited only minimal clinical signs prior to dying, but had massive muscle necrosis at post mortem examination. There were no lesions attributable to usnic acid in other organ systems. It appears that usnic acid is not the toxic agent responsible for X. chlorochroa poisoning.
Impacts
We have ruled out usnic acid as the causative agent of X. chlorochroa poisoning.
Publications
- Dailey, R. N., Raisbeck, M. F., Montgomery, D., Siemion, R. S., Ingram, J. S. (in prep) 2007. Usnic acid toxicity in sheep. J. Wildl. Dis.
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Progress 01/01/05 to 12/31/05
Outputs
Ewes were fed increasing doses of usnic acid in a modified Brownlee up/down in an attempt to reproduce the syndrome seen in elk on the Red Rim during the winter of 2004. At approximately 400 mg/kg BW, feed refusal became apparent and the daily dose was administered together with 250 g of ground alfalfa via stomach tube, split into two doses bid for 7 days. Although no amount of usnic acid caused clinical signs similar to those seen in elk or in sheep fed lichen, doses of 785 mg/kg BW and 625 mg/kg BW caused sudden death 6 and 7 days, respectively, after dosing began. A dose of 480 mg/kg caused no clinical signs, clinicopathological abnormalities or morphologic lesions. Postmortem examination revealed extensive muscle necrosis of appendicular muscles, but none in cardiac, diaphragmatic or axial skeletal muscle. We conclude that the LD50 of usnic acid in ruminants is around 500 mg/kg. We also conclude that, while usnic acid may be 1 factor in X. chlorochroa toxicity, it
is not the only toxin responsible for the syndrome of muscular weakness/paralysis seen in X. chlorochroa intoxication.
Impacts
Usnic acid and Xanthoparmelia lichens figure are used as nutriceuticals, even though there is virtually no information re: their toxicity in mammals. The species X. chlorochroa is also a very common feedstuff in western forests and rangelands. The fact that it is capable of causing massive mortalities in wildlife and livestock is still not completely accepted by many range managers. A better understanding of the toxicity of usnic acid and X. chlorochroa will facilitate rational management decisions in western rangelands.
Publications
- Cook, W.E., Cornish, T.E., Williams, E.S., Brown, B., Hiatt, G., Kreeger, T.J. and Raisbeck, M.F. 2006. Xanthoparmelia chlorochroa intoxication in wapiti (Cervus canadensis). Poisonous Plants and Natural Toxins, CAB Int'l. In press.
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