Ryegrass staggers

Attention! This is a potentially life-threatening condition for your horse. Time is of the essence, contact your veterinarian immediately.Find a Vet

Ryegrass Staggers

Perennial Ryegrass Toxicosis, Lolitrem Toxicity, Ryegrass Poisoning

Ryegrass staggers is a neuromuscular disorder caused by ingestion of perennial ryegrass (Lolium perenne) containing the endophyte fungus Epichloe festucae (Neotyphodium lolii). E. festucae produces several ergot alkaloids and indole-diterpene alkaloids, with Lolitrem B as the main toxin responsible for onset of clinical signs. Ryegrass staggers was first recognized in 1906, involving the muscular incoordination associated with horses and cattle grazing on ryegrass pastures.

The severity and morbidity of staggers varies among horses, with 5 to 75% of other horses in the same pasture, affected. Clinical signs vary from slight trembling in the neck following hard exercise to severe tetanic spasms and collapse.

Most outbreaks of ryegrass staggers occur in Australia and New Zealand. Sporadic cases have occurred in livestock in Europe and the Americas, most of them involving the consumption of contaminated hay. In Japan, there were several cases of ryegrass staggers associated with feeding cattle and horses with contaminated ryegrass straw that had been imported from Oregon.




  • History
  • Clinical signs
  • Physical exam
  • Bioassay



Horse should be removed from infected pasture
Supportive care


  • Make yourself aware of the weeds and plant species that can be invasive in pastures and/or poisonous to horses.
  • Take periodic walks around pastures to check for the presence of potentially poisonous plants
  • Check that hay does not contain dried up poisonous plants
  • If you borrow or hire farm machinery ensure it is clean prior to arriving on your property, the same goes for lending of your own equipment.
  • Quarantine new animals in a separate paddock the first 10 days to 2 weeks after arrival. Weed seeds can be passed through an animal's digestive tract.

Scientific Research

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