Vet Talk: Equine Grass Sickness

Over the next few weeks, we’ll be discussing common spring diseases.

This is your friendly Horse Nation reminder that our articles should not be viewed as medical advice. If you suspect your horse is suffering from equine grass sickness, please consult your veterinarian.

Equine grass sickness damages parts of the nervous system. The cause is unknown, but scientists believe a toxin is involved. Soil borne Clostridium botulinum type C is currently being investigated as a causative agent.

The disease was first diagnosed in 1907 during an outbreak in army remount horses in Scotland. Hundreds of horses died annually from grass sickness in the 1920s, leading historians to believe the introduction of tractors was artificially accelerated as a result.

Grass sickness affects horses, ponies and donkeys. There have also been cases found in a captive zebra and a Przewalski’s horse. The disease also affects wild and domestic rabbits.

It is strongly associated with grazing, though a few cases have been linked to hay. Stressed or overweight animals are often predisposed to the disease. Equine grass sickness is almost always fatal.

Risk factors:

  • LOCATION: Great Britain has the highest number of grass sickness cases in the world. It is also found in northern Europe, especially Sweden, Denmark and Germany, with fewer cases in France, Belgium, Italy, Holland, Norway, Finland and Switzerland. It has also been found in Ireland and two cases have been diagnosed in North America.
  • AGE: The greatest number of cases occurs in horses 2 to 7 years old.
  • SEASON: Most cases are found between April and July with a peak in May. Cool, dry weather with a temperature between 7 and 11°C ( 44 to 51°F) was recorded in a statistically significant number of cases, according to The Equine Grass Sickness Fund.
  • SOIL CONDITIONS: High nitrogen content of soil may be a risk factor. Overcrowding pastures, lack of manure management and bird droppings may also contribute to the disease. Certain properties, or even fields within a property, can be definitively linked to grass sickness cases.

Clinical signs of the disease:

  • GUT PARALYSIS: Look for difficulty swallowing and signs of colic including rolling, pawing at the ground and looking at the flanks. Constipation is another symptom, as well as a grossly distended stomach.

Treatment options:

  • Provide easy to eat high energy foods such as chopped vegetables and concentrates. Appetite stimulants are currently being studied.
  • Frequent grooming and careful blanket management is needed to control sweating and tremors.

How to reduce the risk:

  • Good grass management practices are key
  • Avoid disturbing the soil.
  • Feed hay daily.
  • Make any changes to diet or management regime very slowly.
  • Poo pick manually
  • Avoid over grazing and use rotational grazing techniques with sheep, goats or cattle where possible.

For more information, visit Equine Grass Sickness Fund.

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