Seleniferous Astragalus

Advances in research are performed on the genus Astragalus and about 100 different species have been chemically studied imtill now [249]. The genus appears highly uniform from a chemical point of view, with three kinds of biologically active principles and three diffent groups of toxic compounds. The active constituents are saponins, flavonoids, and polysaccharides, while nitro-compoimds, indolizidine alkaloids and the seleniferous derivatives are included in the poisonous groups. 

Selenium is an essential element but is toxic when excessive quantities are ingested. Exposure of horses is usually through consumption of seleniferous (accumulator or indicator) plants (e.g.. Astragalus spp.). Exposure to high quantities of selenium over a short time causes diarrhea (which is often foul smelling and contains air bubbles), neurological and cardiovascular effects, and respiratory difficulty. Death in these horses is due to respiratory failure. Chronic exposure to low levels of excessive selenium is characterized by hoof abnormalities at the coronary bands and by discoloration and loss of hair. The hoof deformities are painful and cause lameness. 

Highly seleniferous plants have a disagreeable garlic-like odor arising from volatile selenium compounds that are released by the plants. Volatile selenium is also released by nonaccumulator plants such as alfalfa, and the amounts released are qualitatively related to the amounts of selenium within the plant (38). Dimethyl diselenide has been demonstrated as a volatile product of Astragalus racemosus (39). 

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