Equine grass sickness is a life-threatening disease affecting the horse’s nervous system and intestinal tract that has been recognised for more than 100 years. It is particularly prevalent in the UK.

Clinical signs of the disease can vary from sudden death to mild signs, and a full range in between. These signs relate to degeneration of the nerves of the autonomic nervous system; researchers think that the more damaged the nerves are and the greater the number of nerves affected, the more severe the signs.

The acute form of grass sickness occurs suddenly, and results in dullness, dropped eyelids, muscle tremoring, and reduced intestinal motility. This last problem results in colic (abdominal pain) from the trapped gas and fluid which stretches the intestines and stomach. Sometimes these cases have a high temperature and an elevated heart rate. It can be quite frightening that these worrying signs can develop over a matter of hours.

Cases are referred to as subacute if there are similar to above, but signs develop over a day or two. Sadly, acute and sub-acute cases are not able to survive; these horses have to be euthanased on humane grounds.

In the chronic form of grass sickness, the signs do not start as dramatically- they may take a few days to show. Signs of chronic grass sickness include the inability to swallow properly (dysphagia), oesophageal obstruction (sometimes referred to as choke), impaction colic, dry, pelleted faecal balls (sometimes wrapped in dried mucus), dropped eyelids, muscle tremoring, an elevated temperature or heart rate and dullness. These horses have an unusual stance often referred to as an “elephant on a tub” – they tuck all of their legs underneath themselves. Another unusual sign is rhinitis sicca – this is a drying of the lining of the nose which results in crusts inside the nostrils and sometimes a snoring noise. It is possible for chronic cases to survive, but vets will want to see that they are not colicky and can swallow food first – if they cannot do this then their long-term prognosis is very poor.


brown horse looking into lens

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