Locoweed (Astragalus and Oxytropis) poisoning in horses. In: Hovda, L.R., Benson, D., Poppenga, R.H., editors. Blackwell's Five-Minute Veterinary Consult Clinical Companion: Equine Toxicology

Authors: Stegelmeier, Bryan

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 1/5/2021
Publication Date: 1/20/2022
Citation: Stegelmeier, B.L. 2022. Locoweed (Astragalus and Oxytropis) poisoning in horses. In: Hovda, L.R., Benson, D., Poppenga, R.H., editors. Blackwell's Five-Minute Veterinary Consult Clinical Companion: Equine Toxicology. 1st Edition. Hoboken, NJ: John Wiley & Sons, Inc. p. 315-321.

Interpretive Summary: Locoweed poisoning in livestock is reported to be the most expensive poisonous plant problem in the western North America. It is caused by about 20 species of the Astragalus and Oxytropis genera that contain the indolizidine alkaloid, swainsonine. Swainsonine inhibits cellular a-mannosidase and mannosidase II. These enxymes hydrolyze mannose rich polysaccharides, glycoproteins and oligosaccharides. Prolonged swainsonine ingestion produces cellular storage disease and abnormal glycosylation of many different glycoproteins. Clinical disease requires extended enzyme inhibition. Most susceptible livestock require several weeks of poisoning to develop mild neurologic disease. Poisoning affects nearly all body systems and those signs and lesions become more severe with prolonged and repeated poisoning. Clinical poisoning is species specific, but generally includes depression, reluctance to move, dull appearing eyes and rough dull coat that fails to shed properly. Poisoning produces characteristic neuro-visceral cellular vacuolation. When exposure is discontinued most lesions quickly resolve and many animals are useful if they do not have severe neurologic damage. However, many of the neuronal changes are permanent and they become more severe with repeated or prolonged poisoning. Such chronic affected animal lose condition, fail to be productive and may be dangerous to use for work. The objective of this chapter is to present a current update on the pathophysiology, diagnostics and control measure of locoweed poisoning.

Technical Abstract: Locoweed poisoning in livestock is reported to be the most expensive poisonous plant problem in the western North America. It is caused by about 20 species of the Astragalus and Oxytropis genera that contain the indolizidine alkaloid, swainsonine. Swainsonine inhibits cellular a-mannosidase and mannosidase II. These enxymes hydrolyze mannose rich polysaccharides, glycoproteins and oligosaccharides. Prolonged swainsonine ingestion produces cellular storage disease and abnormal glycosylation of many different glycoproteins. Clinical disease requires extended enzyme inhibition. Most susceptible livestock require several weeks of poisoning to develop mild neurologic disease. Poisoning affects nearly all body systems and those signs and lesions become more severe with prolonged and repeated poisoning. Clinical poisoning is species specific, but generally includes depression, reluctance to move, dull appearing eyes and rough dull coat that fails to shed properly. Poisoning produces characteristic neuro-visceral cellular vacuolation. When exposure is discontinued most lesions quickly resolve and many animals are useful if they do not have severe neurologic damage. However, many of the neuronal changes are permanent and they become more severe with repeated or prolonged poisoning. Such chronic affected animal lose condition, fail to be productive and may be dangerous to use for work. The objective of this chapter is to present a current update on the pathophysiology, diagnostics and control measure of locoweed poisoning.