ISSN 2398-2977      

Toxicity: locoweed

pequis
Contributor(s):

Graham Munroe

Synonym(s): Locoism


Introduction

  • Cause: prolonged ingestion of certain species ofAstragalusandOxytropislegumes (locoweeds)   Locoweed (Astragalus / Oxytropis spp)  : contain alkaloids that damage lysosomal enzyme essential in oligosaccharide cellular metabolizm   →   cellular vacuolization.
  • Incidence: commonly found in western North America where horses will ingest locoweeds in early spring or at other times of forage scarcity.
  • Signs: wide range - depend on chronicity of ingestion; particularly neurologic and general loss of condition.
  • Diagnosis: intracytoplasmic vacuoles evident on histopathology.
  • Treatment: mild cases may respond to preventing locoweed ingestion; chronic cases often die or are killed.
  • Prognosis: guarded to poor.

Pathogenesis

Predisposing factors

General
  • Areas of Western, North America where locoweeds can occur.

Specific

  • Scarcity of normal forage:
    • Overgrazing.
    • Early spring.
    • Drought.

Pathophysiology

  • Prolonged ingestion of certain species ofAstragalusandOxytropislegumes (locoweeds): contain alkaloids that damage lysosomal enzyme essential in oligosaccharide cellular metabolism   →   cellular vacuolization.
  • Indolizidine alkaloids swainsonine and swainsonine N-oxide are the toxic principles in locoweeds (similar to Darling Pea (Swainsomaspp) poisoning in Australia).
  • These alkaloids inhibit alpha-mannosidase and lysosomal enzymes esential in cellular metabolism of oligosaccharides.
  • Mannose-rich oligosaccharides accumulate in lysosomes   →   vacuolation and disruption of cellular function.
  • Vacuolation occurs in renal cortical tubular cells as early as 4 days and in the CNS neurons by 8 days.
  • If consumption of the plant stops, the vacuoles will disappear in the early stages of the disease, but if grazing is prolonged, permanent cellular damage occurs.
  • By 30 days most tissues of the body, except muscle, are affected.
  • Vacuolization of axons, glial cells and Purkinje cells of the cerebellum and cerebral cortex   →   neurologic signs.
  • Damage to cells of the liver, pancreas, thyroid and parathyroid glands   →   weight loss and emaciation.
  • Retinal and lacrimal cells can be damaged   →   impaired vision.

Timecourse

  • First vacuolation: 4 days.
  • Most body tissues affected: 30 days.

Epidemiology

  • Locoweeds usually emerge in the early spring before other forage plants are available.
  • Other peak periods are associated with periods of forage scarcity, eg droughts.

Diagnosis

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Treatment

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Prevention

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Outcomes

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Knight A P (1987) Locoweed poisoning. Comp Cont Educ Pract.9, F418 VetMedResource.
  • McIlwraith C W and James L F (1982) Limb deformities in foals associated with ingestion of locoweed by mares. JAVMA 181, 255 PubMed.

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!

 
 
 
 

To show you are not a Bot please can you enter the number showing adjacent to this field

 Security code