Microbial degradation of usnic acid in the reindeer rumen
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Reindeer (Rangifer tarandus) eat and utilize lichens as an important source of energy and nutrients in winter. Lichens synthesize and accumulate a wide variety of phenolic secondary compounds, such as usnic acid, as a defense against herbivores and to protect against damage by UV-light in solar radiation. We have examined where and to what extent these phenolic compounds are degraded in the digestive tract of the reindeer, with particular focus on usnic acid. Three male reindeer were given ad libitum access to a control diet containing no usnic acid for three weeks and then fed lichens ad libitum (primarily Cladonia stellaris) containing 9.1 mg/g DM usnic acid for 4 weeks. Usnic acid intake in reindeer on the lichen diet was 91–117 mg/kg BM/day. In spite of this, no trace of usnic acid or conjugates of usnic acid was found either in fresh rumen fluid, urine, or feces. This suggests that usnic acid is rapidly degraded by rumen microbes, and that it consequently is not absorbed by the animal. This apparent ability to detoxify lichen phenolic compounds may gain increased importance with future enhanced UV-B radiation expected to cause increased protective usnic acid/phenol production in lichens.
KeywordsReindeer Lichens Usnic acid Phenolics Rumen
We are grateful to Hans Edvin Lian and Magnus Folkow for all their help with the animals and to Jennifer Addison for her help with the chromatographic analyses. This project was funded by The Reindeer Husbandry Research Fund (Project A5299). It is linked to the framework of the International Polar Year as part of the IPY consortium IPY no. 399 EALAT: Climate change and reindeer husbandry.
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