Equine Grass Sickness

Equine Grass Sickness (EGS) is a rare but debilitating disease which results in damage to the nerves supplying the gut, resulting in its paralysis from the oesophagus onwards.

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The cause of Equine Grass Sickness (EGS) is still unknown, but is thought to be due to the ingestion of toxin from pasture.

Which Equines Are Affected By Grass Sickness?

It can occur in equids of any age, but the highest number of cases are seen in those between the ages of 2 and 7 years. It has been suggested that the reduced cases seen in older animals may be due to the development of some resistance to the disease over years.

Cases have been reported year round, but the highest number of cases are generally seen between April – July. Affected horses are usually receiving significant turnout, and animals which have been grazing the pasture for less than 2 months are considered at higher risk.

Risk Factors Of EGS

Specific risk factors are unknown, but over grazing/crowding, mechanical disturbance, stress and changes in weather conditions have been suggested.

Types Of Equine Grass Sickness

There are 3 main types, Acute, Sub-acute and Chronic.

Acute Equine Grass Sickness

Symptoms of acute EGS include:

  • Sudden onset severe signs of colic
  • Difficulty swallowing and drooling of saliva
  • Stomach contents pouring out the nose.

The symptoms are severe and many horses die or are euthanised at an early stage.

Other symptoms include patchy sweating and muscle tremors.

Diagnosis is made by sampling the nerves supplying the intestine, but the prognosis is hopeless.

Sub-acute Equine Grass Sickness

Symptoms of sub-acute EGS are similar to acute EGS, but are less severe. Affected animals may still eat small amounts, but usually deteriorate within a week and require euthanasia.

Chronic Grass Sickness

The symptoms come on more slowly and low grade, intermittent colic may be the only symptom. Often the animal’s appetite is reduced, and usually accompanies rapid weight loss and reduced ability to swallow.

Diagnosing Equine Grass Sickness

Diagnosis EGS is challenging, as affected animals may only show a few of the known symptoms, and it can be very difficult to distinguish between EGS and other causes of colic or weight loss.

Definitive diagnosis can only be reached by sampling the nerves of the intestine, either under general anaesthetic or at post mortem, so on many occasions this is not reached – there is no definitive test in the awake, live horse.

Treating Equine Grass Sickness

Acute and subacute EGS is not treatable, and affected animals should be euthanised on welfare grounds. Attempt at treatment can be made in some chronic cases if the animal is not in pain and still maintains some appetite and interest in life, although the prognosis of long term survival is guarded.

Treatment involves feeding high energy, palatable and easily swallowed feeds and constant nursing.

Preventing Equine Grass Sickness

It is extremely difficult to give appropriate prevention advice when the cause is unknown, but avoiding pasture which has had cases, and stabling horses at higher risk times has been suggested.

The Grass Sickness Research Team, and others are currently undertaking several lines of investigation. 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.

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