Cliffe Equine's home page
  • Call our surgery01323 815120

Grass Sickness

What is it?

Equine Dysautonomia (aka Grass Sickness) is a disease affecting horses, ponies, and donkeys in which there is damage to parts of the nervous system which control involuntary functions, producing the main symptom of gut paralysis. Grass sickness is thought to be caused by the toxin produced by the soil-borne bacterium, Clostridium Botulinum, occurring almost exclusively in horses with access to grass. 

Despite ongoing research there is still a limited understanding of the disease, however high risks are believed to include:

  • Sudden weather changes can heighten risk, with most cases occurring during cold, dry weather. May-July and Autumn are high-risk months.
  • High-risk horses are most commonly between 2-7 years old in good body fat condition.
  • Dietary changes, movement to new pastures, frequent worming can increase risks.
  • Pasture disturbance e.g., construction work, ditch digging and mole hills
  • Grazing on high soil nitrogen and sand or loam soil types have been found at affected locations.

There are two categories of grass sickness, based on the presenting symptoms: 


Acute cases are severe. Horses suffering from acute signs of grass sickness cannot be saved and should be euthanised on welfare grounds as soon as the diagnosis is clear. Signs of acute cases are:

  • Colic
  • Reflux of green fluid coming out of the nose from the stomach
  • Dysphagia (difficulty swallowing)
  • Muscle tremors
  • ‘Patchy’ sweating patterns
  • Reduced faecal output
  • Lethargy & distress


Cases have a guarded prognosis, but with intensive nursing can be managed. Signs of chronic cases are:

  • Signs develop slowly
  • Weight loss
  • Tucked up
  • Difficulty swallowing
  • Colic signs
  • Sweating
  • Tremors
  • ‘Snuffling’ noise when breathing due to mucus build up

Ongoing studies have revealed 60% of chronic cases in Scotland survived, compared to 45% of cases in England. Grass sickness has never been found in Ireland, despite the similar climate.


  • Minimise exposure to pastures where previous cases have occurred
  • Minimise any pasture/soil disturbance (e.g., harrowing/mechanical faeces removal/pipe-laying/construction work etc.)
  • Minimise soil exposure (close grazing)
  • Avoid any sudden changes in diet
  • Worm egg count and worm accordingly, avoid blanket worming
  • Regular poo-picking

Grass sickness is hard to diagnose. The only definitive diagnostic is by taking a sample from the small intestine for testing, however this sample can only be obtained under surgery.

If your horse starts displaying any of the signs of grass sickness, call your veterinarian IMMEDIATELY. 

Proceeds from our Inside Equine Colic client evening taking place on Tuesday 15th November 2022 will be donated to The Equine Grass Sickness Fund for continued research.