All you Need to Know About Grass Sickness

So you’ve just about got past mud fever and strangles season (although yes, we know they can occur at any time of year!!) , and guess what, there’s another looming disease to worry about – this time it’s grass sickness! Although cases occur in every month of the year, most are seen between April and July, with a peak in May. In some years this is followed by a second peak in autumn. Here are a few key things you need to be aware of when it comes to this disease.

What is Equine Grass Sickness (EGS)?

Equine grass sickness (EGS) is a weakening and often fatal disease in horses, ponies and donkeys. Great Britain has the highest number of cases of grass sickness in the world.

The disease is displayed as impaired activity in the gut due to nervous system damage. This damage is to a part of the nervous system that controls involuntary functions, such as breathing and sweating.

There are three types of Grass Sickness: Acute (AGS), Subacute (SAGS) and Chronic (CGS).

AGS has a severe and sudden onset. Horses with Acute Grass Sickness die or require euthanasia within 48 hours of getting it. Sadly, there is no treatment for this form of the disease.

SAGS cases show milder signs than acute cases, with affected horses surviving beyond 2 days. However, they often die or require euthanasia within just a week. As with AGS, there is no treatment for this form of the disease.

What causes Grass Sickness?

The cause is not really known, but strong evidence suggests that it is a bacteria in the soil, Clostridium botulinum (type C), which brings it on. It is thought that a toxin produced in the horse’s gastrointestinal tract (digestive system) causes damage to the nervous system, interrupting the normal gut movements and stopping digestion proceeding. This then leads to the clinical signs typically seen. Grass sickness does not appear to be contagious.

What are the signs of Grass Sickness?

  • Rapid and severe weight loss
  • Tucked up abdomen
  • Dry, crusty nose
  • Drooping eyelids
  • Slightly elevated heart rate
  •  Muscle tremors
  • Patchy sweating
  • Reduced appetite
  • Slight difficulty swallowing

Is it curable?

In truth – not easily, if at all. Treatment should not be considered for acute or subacute cases and careful case selection is needed for the treatment of chronic cases. Sadly, the nursing of these cases is not always successful, but if the animal is not in too much pain, can still eat a small amount and is still interested in life, treatment may be attempted. The management of such a case is time consuming and emotionally difficult. Recovery can take a long time and the outcome is unpredictable.

What type of horse can get EGS?

The greatest number of cases occurs in 2 to 7 year olds with a peak at 3 to 4 years. Older horses seems to get it less which suggests they may have built up a resistance.

How can I prevent my horse getting EGS?

Preventative measures to minimise the risk of EGS include:

• Avoiding grazing previously affected fields

• Avoiding pasture disturbance

• Avoiding feed changes
• Reducing horse movements between premises/ pastures


The Equine Grass Sickness Fund is the only registered charity in the UK raising funds specifically for research into grass sickness. EGSF is dedicated to supporting and advancing research into grass sickness and further improving the treatment of chronic cases. You can find plenty more info about this disease on their website

Leave a Reply

Your email address will not be published. Required fields are marked *