New research into equine grass sickness at the University of Liverpool could
lead to horses being routinely vaccinated against the disease in the UK.
Grass sickness was first identified around 100 years ago but so far scientists
have struggled to understand the disease and identify what causes it. It is
usually fatal and presents itself in two different ways: either as severe
colic (causing a horse to roll and sweat through abdominal pain caused by
distension of the intestine) or as loss of weight 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' may, however, 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.
A new study, based at the University's Equine Hospital, Leahurst, on the Wirral and
funded by The Home of Rest For Horses, has found grass sickness is strongly associated
with low antibody levels to the bacterium Clostridium botulinum. The findings may now
lead to routine vaccination against the bacterium for horses in the UK.
Dr Chris Proudman
Dr Chris Proudman, 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."
He added: "We are grateful to The Home of Rest For Horses who have made the study possible."
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 Clostridium 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 worming 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. Dr Proudman commented: "After nearly 100 years of research effort, prospects
for the effective prevention of equine grass sickness have never been better."
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Dr Chris Proudman
Brigadier Paul Jepson
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