Equine grass sickness, also known as equine dysautonomia, is a neurological disease of horses. It can affect horses of any breed, sex or age, with disease occurring mostly in horses aged 2-7 years old. It appears to affect different geographical areas within the UK, with the east of England thought to be the most affected. However, cases have been reported all over the UK.

The exact cause of grass sickness is still uncertain, but current research has led to a focus on a soil-dwelling bacterium clostridium botulinum. One type of this bacterium causes botulism in horses, but a different type, type C, is thought to be involved in the onset of grass sickness. The toxin produced by this bacteria damages nerves that control involuntary functions, leading to symptoms of colic due to the movement of the gut slowing down or stopping. Other symptoms include weight loss, difficulty swallowing, muscle tremors, drooping eyelids and excessive salivation.

Diagnosis of grass sickness can be difficult as some of the symptoms, such as colic, can be caused by a number of different diseases. Diagnosis is therefore usually made based on the symptoms the horse shows and ruling out other possible causes. The only way to make an exact diagnosis is by taking a sample of the small intestine and examining it under a microscope. This is not carried out in most cases of grass sickness as it requires the horse to undergo surgery.

There are three types of grass sickness, which overlap slightly in their symptoms; acute, subacute and chronic. Horses with acute grass sickness, symptoms appear very suddenly and can be quite violent, with signs of colic, reflux of fluid from the stomach and difficulty swallowing becoming apparent. Sadly, there is no treatment for this form of the disease and horses usually have to be euthanised to prevent further suffering. Subacute grass sickness shows similar signs, but also tend to require euthanasia within one week. Horses that survive longer than 8 days fall into the chronic category, and in some cases long term intensive nursing can lead to a successful outcome for these horses.

Horses with chronic grass sickness show the classic base narrow, “elephant on a drum” stance and a tucked up appearance of the abdomen. Nursing and treatment of these cases can be intense and last for many weeks and can still be unsuccessful despite every effort being made.

For more information on Equine Grass Sickness, visit the Equine Grass Sickness Fund website http://www.grasssickness.org.uk/.