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Toxicity: fescue grass

ISSN 2398-2977


Synonym(s): Tall fescue toxicosis

Introduction

  • Cause: ingestion of infected pasture or conserved forage by pregnant mares especially in early/late pregnancy: endophytic infection of Tall Fescue grass by fungus Neotyphodium coenophialum →  production of ergopeptine alkaloids including ergovaline which have a number of vasoactive and dopaminergic actions including inhibition of prolactin secretion.
  • Signs: a wide range of reproductive abnormalities including agalactia, prolonged gestation, dystocia, thickened or retained placenta, decreased reproductive efficiency and decreased fetal/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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Presenting signs

Geographic incidence

  • Southeastern USA.
  • Northwestern USA.
  • Rest of USA.

Age predisposition

  • Neonate.
  • Adult.

Gender predisposition

  • Mares and their foals.

Breed/species predisposition

  • Broodmare.

Cost considerations

  • Loss of foal.
  • Infertility in Broodmare.

Pathogenesis

Predisposing factors

General

  • Grazing of pastures containing Tall Fescue grass.

Specific

  • Tall Fescue grass infected by the specific fungus Neotyphodium coenophialum.

Pathophysiology

  • Endophytic infection of the Tall Fescue grass by the fungus Neotyphodium coenophialum. The fungus lives in the plant and the seeds.
  • Production by fungus of ergopeptine alkaloids including ergovaline, which have vasoactive and dopaminergic actions.
  • 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 Female: agalactia / hypogalactia.
  • 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

  • Neotyphodium coenophialum spends 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 Sci 73, 899-908 PubMed.