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Equine Grass Sickness Linked to Clostridium Botulinum

Horse Health Press Release

A new study completed at the University of Liverpool in the United Kingdom and funded by The Home of Rest For Horses has revealed that grass sickness is strongly associated with low antibody levels to the bacterium Clostridium botulinum. The findings might lead to routine vaccination against the bacterium in U.K. horses.

Grass sickness was first identified around 100 years ago, but scientists have struggled to understand the disease and identify its cause. Few or no cases have been found in the United States. The disease usually is fatal and presents itself in two different ways--either as severe colic or weight loss and difficulty eating. Both manifestations of grass sickness are as a result of nerve damage to the intestine.

Grass sickness is a seasonal disease, with the majority of cases occurring in the spring. The name "grass sickness" might be misleading as scientists now suspect the disease has less to do with grass than was originally thought--the name was coined many years ago when scientists understood much less about the disease.

Chris Proudman, MA, Vet MB, PhD, CertEO, FRCVS, of the U.K.'s University of Liverpool, and senior lecturer in equine surgery, said, "This research is important because it confirms the link between grass sickness and Clostridium botulinum. This link, first proposed in the 1920s, was recently re-evaluated by researchers at the University of Edinburgh. Our study builds on this previous work and demonstrates protection against the disease in horses with high antibody levels against the bacteria. This strongly suggests that vaccination may be effective in preventing the disease."

The new research, published in the Equine Veterinary Journal this week, involved the study of 66 horses with grass sickness in 58 different premises.

Blood samples were taken to evaluate antibody levels against C. botulinum, and compared to antibody levels in unaffected horses from the same premises. Information on management practices was analysed along with samples of soil and pasture in order to identify factors that altered the risk of grass sickness occurring.

A number of new risk factors were identified including change of feed type or quantity and the use of the deworming agent ivermectin--all of which make horses more susceptible to grass sickness. The use of hay or haylage as a feed was found to protect against the disease.

Paul Jepson, Chief Executive of The Home of Rest For Horses and a veterinary science graduate of the University of Liverpool, said, "The Home of Rest for Horses is delighted to be associated with this long-awaited breakthrough in understanding the cause of grass sickness. There is now real hope for the development of an effective vaccine."

The research team that collaborated on the project is now exploring potential Clostridial vaccines for evaluation in horses. Proudman commented, "After nearly 100 years of research effort, prospects for the effective prevention of equine grass sickness have never been better."