by Perry McCarney

Created on: February 11, 2010

Grass sickness is an extremely serious disease in horses and ponies; medically it is called equine dysautonomia (ED). The acute forms, that rapidly develop, are almost always fatal; so much so that euthanasia is nearly always the recommended treatment. Horses suffering from chronic ED have about a 50:50 chance of recovery, but such a recovery takes about a year of dedicated nursing.

(For details on clinical signs and treatments please see the articles under Helium's title "Grass sickness in horses: Symptoms and treatment.")  

Preventing our horses developing grass sickness in the first place is therefore the best thing we can do for them. And that may be as simple as supplementing their diet.

Equine dysautonomia is called grass sickness for a very good reason. While it may occur in any horse after weaning, it is most common in horses aged between two and seven years that are fed solely on pasture. Occurring most frequently in temperate zones during Spring and early Summer, when horses are often put out to pasture after over-wintering in stables.

Therefore, adding grain or oats to our horse's grass diet twice a week, will significantly reduce the likelihood of their contracting ED. Regular treats such as equine biscuits or the old favorites, apples, carrots and sugar lumps, would also be a good idea. It is possible that the abrupt change in diet when horses are put out to pasture from winter stabling is a contributory factor in its development.  

Research has indicated that there is a possible correlation between ED and a bacterial infection of Clostridium botulinum type C. This species of bacteria produce neurotoxins that may interfere with the autonomic nerve signals controlling the smooth muscle function of the gastrointestinal tract. Horses with a developed systemic immunity to C. butulinum type C appear to be less likely to develop ED than those that do not. Vaccination against C. butulinum type C should therefore be considered for horses grazing in fields or regions where a high incidence of ED has occurred historically. Blood tests can determine whether a horse already has significant immunity before a vaccination is given. This should only be considered in consultation with your veterinarian.

An alternative where multiple horses and paddocks are owned or used, such as a horse ranch, is to regularly rotate the animals through different paddocks. Particularly if there is an historical occurrence of ED related to particular paddocks of the ranch.

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