The Toxicology of the Astragalus genus

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Members of the genus Astragalus are known by a number of different names. Those most widely used are locoweed and milkvetch. There are over 2000 species in this genus that are known currently, of which many are known to carry various toxins. (Williams, 1984) They can be found in North and South America, Asia, Europe, Northern Africa and Australia. There are nearly 400 species in North America whose range extends over most of most of the continent. (Ralphs, 1992) They are predominantly in the central plains and grassland regions of the United States where they are the most common of the Leguminosiae. Due to their range and toxicity, livestock poisoning by locoweed is the most widespread toxic plant problem in the western U.S.,(Ralphs, James, Nielsen, Baker, Molyneux, 1988) costing millions of dollars both in livestock loss and in cost of plant control (Williams, 1984) Despite the unpleasant effects of Astragalus poisoning, animals often become habituated to eating, fueling their further intoxication by the plant.(Ralphs, Panter, James, 1990)

Astragali poison in three main ways:

With the indolizidine alkaloid swainsonine as in the case of A. lentiginosus and A. lusitanicus
With the nitropropanol bearing glycoside miserotoxin as in the case of A. miser

AND
With toxic levels of selenium metabolites (Se) as in the case of A. bisulcatus

In this series of web pages I'd like to present a compilation of some of the toxicological information available on Astragalus. This will include a description of the specific toxicants named above, their modes of action, the physiological effects and the common symptoms of poisoning by swainsonine, miserotoxin and Se excess, as well as some general effects of Astragalus intoxication. Also in these pages will be some means to identify Astragalus, (whenever I could find them) and that researchers have explored to control poisoning by these plants.

References and Citations

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These pages were created by Mike Scimeca as a term project for Dr. Dan Brown's class on Nutritional Toxicology in Cornell's Animal Science department. I'd appreciate any comments that you have on these pages.