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"Poisonous" does not mean deadly. Some manifestations of toxicity are subtle. The dose, as always, determines if a plant is safe source of nutrients or a toxic hazard.

Selenium Poisoning

These are some of the Astragalus species that carry high levels of selenium which have a wide enough range and large enough population to be of concern:

  • A. bisulcatus
  • A. pattersonii
  • A. pectinatus
  • A. racemosus
(James and Walsh, 1992)

These plants usually have a characteristic musky odor due to the volatile dimethyl selenium compounds that they contain, generally causing animals to avoid them. However, under certain conditions, animals will turn to them as a source of food.

Selenium toxicity causes two main syndromes:

These two syndromes are not necessarily independent of one another. An animal may have only symptoms of one or the other or a combination of the symptoms of both. Both are associated with cardiac and skeletal muscle damage as well as hepatic damage.

Blind Staggers

This syndrome may occur within a brief period (a few days to a few weeks) after the animal has begun to take in very high dietary levels of selenium. The symptoms of this condition are: impaired vision, a depressed appetite, and wandering in circles. Without removal of the high Se intake, this can progress to varying amounts of paralysis and finally death from respiratory failure.

Alkali Disease

This is a more chronic disease associated with lower level and longer duration intake of selenium. It's characterized by emaciation, loss of hair, deformation and shedding of hooves, loss of vitality and erosion of the joints of long bones.

Selenium Metabolites
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More information on Selenium poisoning