Locoweed Toxicosis

Locoweed Toxicosis



Basic Information image



Definition




• Locoweeds (Astragalus and Oxytropis species) are native plants of North America that can cause a variety of systemic effects, especially on the central nervous system (CNS) and reproductive system. They can also affect the heart, intestinal system, and lymphocytes of horses and other livestock species.


• In addition, some locoweed species are selenium accumulators.



Synonym(s)


Locoism, a term derived from the Spanish word loco, meaning “crazy,” describes the abnormal neurologic signs in horses poisoned by locoweeds (milk vetches) of the Astragalus and Oxytropis species.



Epidemiology



Species, Age, Sex


Horses, livestock, and wild ruminants are susceptible. Nursing young are most susceptible because the toxic alkaloid in locoweeds is passed through the milk.



Risk Factors




• Toxic at all growth stages, locoweeds are most palatable to horses in the spring when the plants are in flower. Some toxicity is retained in the dried plants.


• Although not truly addictive, horses find locoweeds palatable and may seek them out in preference to other forages, especially when the plants are in flower.



Geography and Seasonality




• More than 350 native species of locoweeds belong to the Astragalus and Oxytropis genera in North America. Relatively few species are important toxicologically.


• Geographically, the toxic species of locoweed are concentrated in the intermountain and southwestern United States. Locoweeds are short-lived perennial legumes that reproduce from seeds that can remain viable in the soil for more than 50 years (Figures 1 and 2).


image

FIGURE 1 White locoweed (Oxytropis sericea).


image

FIGURE 2 Spotted or blue locoweed (Astragalus lentiginosus).



Clinical Presentation



Disease Forms/Subtypes


Depending on the species of Astragalus and Oxytropis, three distinct toxins may be present: swainsonine, nitrotoxins, or selenium.



History, Chief Complaint


Changes in temperament, behavior, incoordination, and weight loss are typical presenting signs



Etiology and Pathophysiology




• Locoism results from the consumption of locoweeds infected with an endophyte (Embellisia spp.) that produces the indolizidine alkaloid swainsonine.


image Swainsonine inhibits α-mannosidase, an enzyme critical in the metabolism of oligosaccharides.

image Complex sugars accumulate in cells with resulting cellular dysfunction and death.
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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Locoweed Toxicosis

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