Locoweeds: Assessment of the Problem on Western U.S. Rangelands
The toxic species of Astragalus cause three different syndromes of poisoning according to the toxin they contain. These three groups are: nitro-containing Astragalus, acute and chronic poisoning; selenium-accumulating Astragalus, acute and chronic poisoning; and swainsonine-containing Astragalus and Qxytropis, chronic poisoning. The economic losses due to the presence of locoweed on rangelands are very difficult to measure. Other losses due to locoweed may include emotional or sentimental losses, such as the loss of the family ranch, a favorite horse, or a child's pony. Management time and effort expended to prevent locoweed losses, as reported in the case studies, can be a substantial cost to a rancher. Most locoweeds are biennials that flourish periodically under appropriate environmental conditions. Thus, periodic regional problems usually occur, causing heavy livestock losses. Tradition and the accounts of many livestock producers would indicate that habituation may be a factor in locoweed poisoning, but current research has cast some doubt on this aspect of locoweed intoxication.