Equis ISSN 2398-2977

Toxicity: fescue grass

Synonym(s): Tall fescue toxicosis

Contributor(s): Graham Munroe

Introduction

  • Cause: ingestion of infected pasture or conserved forage by pregnant mares especially in early/late pregnancy: endophytic infection of Tall Fescue grass by fungusAcremonium coenophialum  →   production of ergopeptine and pyrridolizidine alkaloids having a number of vasoactive and dopaminergic actions including inhibition of prolactin secretion.
  • Signs: a wide range of reproductive abnormalities including agalactia, prolonged gestation, dystocia, decreased reproductive efficiency and decreased foal survival.
  • Diagnosis: identification of infected pasture or seed is essential to diagnosis and preventative regimes.
  • Treatment: symptomatic but stimulation of prolactin secretion can be effective if initiated early.
  • Prevention: most effective approach to dealing with the disease involves avoiding grazing of infected fescue pastures especially early/late in pregnancy; replacement or dilution of pasture or diet by other forages.
  • Prognosis: guarded.
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Pathogenesis

Pathophysiology

  • Endophytic infection of the Tall Fescue grass by the fungusAcremonium coenophialum.
  • Production by fungus of ergopeptine and pyrrolizidine alkaloids.
  • Vasoactive and dopaminergic actions with pyrrolizidine alkaloids inhibiting prolactin secretion.
  • Wide range of pathologic changes in the pregnant mare and foal.
  • The alkaloids have 2 actions:
  • Vasoconstrictive (ergopeptine).
  • Dopaminergic.
  • Peripheral vasoconstriction is associated with increased incidence of laminitis   Foot: laminitis  .
  • Dopaminergic alkaloids inhibit prolactin secretion by the anterior pituitary gland.
  • Mares grazing Tall Fescue pastures during late pregnancy have decreased serum concentrations of prolactin and progesterone and increased estrogen.
  • The decreased hormone levels   →   agalactia.
  • The diverse range of abnormalities in the pregnant mare and foal may be related to the common dopaminergic actions, but the mechanism is unclear.

Epidemiology

  • Acremonium coenophialumspends its entire life-cycle within the vegetative parts of the Tall Fescue and it is impossible to visually recognize an infected plant.
  • Infection rates in pasture vary but >80% is generally regarded as posing a severe threat to pregnant mares; rates as low as 5% have been associated with problems.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Cross D L et al (1995)Equine fescue toxicosis. Signs and solutions.J Anim Sci73899-908 PubMed.


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