Equine Grass Sickness



What is grass sickness?


Equine grass sickness, or Equine Dysautonomia, is a devastating disease that can affect horses of all ages and type. This complex disease attacks your horse’s nervous system, compromising their ability to swallow and preventing the movement of food through the digestive tract. It can result in a build-up of fluid in the stomach and small intestine, dehydration, and impaction of the large intestine.

EGS is most often seen in the months of May through to September and in animals of 1 to 9 years of age, but it can be seen at all times of the year and in all ages of animals.


What causes grass sickness in horses?


The definitive cause of the disease is unknown but is likely to be a combination of factors – the currently favoured theory under investigation is the possible involvement of Clostridium botulinum, the bacteria that causes botulism.

What are the equine grass sickness signs to look out for?

Acute grass sickness

In acute cases you’ll see severe signs of colic, including rolling, pawing and looking at the flanks, drooling and difficulty swallowing. Your horse might also:

  • Look bloated and is likely to be constipated
  • Foul-smelling nasal discharge
  • Pass small, hard poos with a ‘cheesy’ coating of mucus
  • Muscle tremors and patchy sweating

Sub-acute grass sickness

Sub-acute cases show similar signs, but with less severity. Accumulation of fluid is less likely to occur, but they are likely to be:

  • Sweating
  • Mild to moderate colic and difficulty swallowing
  • Muscle tremors
  • Rapid weight loss

Chronic grass sickness

With chronic cases, the signs come on more slowly and only some cases show mild, intermittent colic. Horses are likely to have a reduced appetite and will have difficulty swallowing, but they won’t drool, accumulate fluid in the stomach or suffer from severe constipation. The most important indicators to look out for are:

  • Reduced appetite and difficulty swallowing
  • Rapid and severe weight loss

Grass sickness prevention advice

As it’s still unclear what causes the disease, it’s difficult to know for certain how to prevent it. But current research suggests that changing your management practices to avoid the known risks is the best place to start.

  • Avoid grazing areas at the same time of year where there have been previous cases of grass sickness, especially youngsters
  • Also avoid grazing pasture with a history of grass sickness cases where there has been recent soil disturbance, for example, from harrowing
  • Minimise soil exposure by moving horses before grazing gets too short or fields are poached
  • Avoid sudden changes to your horse’s diet
  • Co-graze with ruminants such as sheep
  • Poo-pick regularly by hand
  • Feed supplementary forage alongside grazing, such as hay or haylage
  • Avoid the overuse of ivermectin based wormers

Grass sickness is an emergency so if your horse shows any of the above symptoms, please call the practice immediately.