Scottish Researchers on the Hunt for Cause of Equine Grass Sickness

Equine grass sickness (EGS) is an often fatal neurologic disease affecting primarily young grazing horses, and a team of researchers from the University of Edinburgh in Scotland are working to find its cause. Their findings regarding bacteria in the feces of affected horses compared to non-affected horses were recently published in the Equine Veterinary Journal.

Since its first reported occurrence in Scotland, grass sickness has occurred in most northern European countries and in South America. Horses with more severe forms of the disease experience colic, difficulty swallowing, reflux of stomach contents, excessive salivation, high heart rate, impacted intestines, muscle tremors, and patchy sweating. Horses with the less severe form experience sudden and extreme weight loss, drying of the nasal membranes, and difficulty in swallowing. Only mild cases that receive intensive care survive.

The clinical signs of EGS are largely caused by degeneration of specific nerve cells responsible for controlling involuntary body functions. The poor prognosis associated with the disease is largely attributable to an impairment that prevents food from moving through the intestinal tract. Researchers have proposed that the nerve cell degeneration results from a neurotoxin and that toxins produced by the bacterium Clostridium botulinum might also be a cause.

Recently, researchers tested manure samples from horses with EGS and compared them with samples from healthy horses and those suffering from colic that did not have EGS.

"We found that almost half of the dung samples from EGS cases contained the bacteria C. perfringens, whereas it was detectable in only 5% of samples collected from the other horses," explained Bryony Waggett, HND, BSc, a research assistant studying the disease at the University of Edinburgh.

However, Waggett said this finding does not guarantee that this bacterium causes the disease (it's possible, even likely, that slow gut motility associated with the disease permitted an overgrowth of certain bacteria). University researchers continue to investigate whether high C. perfringens levels cause or result from grass sickness.

"If we knew what was causing this disease, then we could find some way of hopefully preventing it, for example by vaccination," said Waggett. "Current attempts to minimize disease occurrence rely on avoiding certain factors that previous studies have identified as being associated with an increased risk of disease."

Suggestions for disease prevention include the following:

  • Minimize pasture or soil disturbance,
  • Avoid any sudden changes in diet,
  • Encourage co-grazing with ruminants,
  • Cut the pasture grass regularly,
  • Regularly remove manure by hand rather than with mechanical equipment, and
  • Supplement forage feeding with hay or haylage.

More information can be found on the Equine Grass Sickness Fund website.

The study, "Prevalence of Clostridium perfringens in faeces and ileal contents from grass sickness affected horses: comparisons with 3 control populations," was recently published in the Equine Veterinary Journal. The abstract can be viewed at PubMed.

About the Author

Marie Rosenthal, MS

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