Equis ISSN 2398-2977

Toxicity: bracken

Synonym(s): Pteridium aquilinum poisoning, Bracken staggers

Contributor(s): Graham Munroe

Introduction

  • Cause: ingestion of bracken fern (Pteridium aquilinum  Bracken Fern (Pteridium aquilinum)  ).
  • Signs: progressive weakness/incoordination (staggers)   →   recumbency.
  • Diagnosis: history, signs, response to thiamine treatment.
  • Treatment: thiamine supplementation.
  • Prognosis: guarded.
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Pathogenesis

Etiology

  • Bracken contains the enzyme thiaminase in all parts of the plant.
  • Thiaminase is not destroyed by drying the plant and contamination of hay is a source of the plant.
  • Also reported to contain heat-stable antithiamine factor, a factor capable of inducing bone marrow suppression and a beta-glucopyrranoside which may enhance the release of endogenous histamine.
  • Ingested thiaminase   →  clinical thiamine deficiency syndrome.
  • Thiamine plays and integral role in carbohydrate, fat and protein metabolism.
  • Thiamine deficiency interupts cellular energy processes and limits certain metabolic pathways resulting in the systemic accumulation of a variety of metabolites.
  • Initially affects the peripheral motor nerves causing gradual myelin degeneration, but this is progressive throughout the nervous system.

Predisposing factors

General
  • Toxicity any time of the year but consumption is more likely in late summer and autumn, when other forage is scarce.
  • Individuals may acquire a taste for the plant in pastures or in bedding.

Pathophysiology

  • Bracken is not usually palatable and will generally only be eaten by horses if food is scarce.

Diagnosis

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Treatment

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Prevention

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Kelleway R A & Geovjian L (1978) Acute bracken fern poisoning in a 14-month-old horse. Vet Med Small Anim Clin 73 (3), 295-296 PubMed.


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