The horse world is mystified by a frequently fatal disease called equine grass sickness (EGS) which affects grazing horses, ponies and donkeys. At her Balmoral Estate the Queen has lost several of her prized Highland ponies to the disease in the last two years, including her two breeding stallions. Scotland and the north east of England seem to be the areas worst affected, but EGS can strike anywhere and the UK has the highest number of cases compared to other countries in the world.
The British Horse Society is funding research into EGS, which involves the setting up of a biobank so that samples from affected horses can be analysed. Researchers suspect that a bacterium in the soil creates a toxin (linked to botulism), but this does not explain why some horses get the disease and others, on the same pasture, remain perfectly healthy.
Other factors affecting the incidence of EGS are thought to be climactic conditions (cold, frosty nights and hot, dry days), soil disturbance, and the presence of certain fungi. Why the disease affects certain animals and not others could be down to an hereditary disposition, stress, gut microbes and nutritional deficiencies in a horse’s diet.
EGS can affect any horse, pony or donkey but it is most frequently seen in young adult horses between two and seven years old. It is a particularly distressing disease, and renders the horse unable to eat or drink, or to be able to defecate. Their cut effectively becomes paralysed.
Acute signs of the disease can occur rapidly, and include:
- signs of colic with no gut sounds
- difficulty swallowing and excessive salivation
- distended stomach filled with fluid
- drooping eyelids
- runny nose (as the contents of the stomach pour out)
- sweating
- muscle tremors.
Due to the hopeless prognosis for survival, horses usually have to be euthanized to prevent further suffering. There is currently no cure for EGS, or vaccination to prevent it, but there are some steps that owners can take to reduce the risk of the disease such as:
- minimizing grazing where an EGS case, or suspected case, has occurred
- minimizing soil disturbance (for example, removing droppings manually rather than using a harrow)
- using a worm-test kit (easily available on the internet) rather than routinely worming with chemicals
- co-grazing with ruminants such as sheep.
Thankfully, the Isle of Man is not a hot-spot for EGS, and cases here are very rare, but the toxin could migrate or mutate in time to come. Irrespective of the current risk, island horse owners should carry out routine pasture management practices, as outlined above, to keep their horses in general good health.