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9
EQUINE MATTERS
GRASS SICKNESS
Equine grass sickness (EGS) is a debilitating and usually
fatal degenerative disease of the neurological system
affecting grazing horses, ponies and donkeys.
Emma Houghton BVetMed Cert AVP(EM) MRCVS,
Endell Equine Hospital
The UK has the highest incidence of EGS
worldwide with studies showing there are
specific high-risk areas throughout the country.
EGS was first reported in 1909 in Scotland
and since then numerous theories have been
proposed for the cause. Research in the past
20 years has been directed towards the
association with Clostridium botulinum type
C and its neurotoxins. Studies have shown
that horses with EGS have lower antibody
titres to C. botulinum type C. In addition, it
has been shown that horses with higher
antibody titres have a reduced risk of
developing the disease. It is not believed to
be the ingestion of the preformed C. botulinum
type C neurotoxins which result in the
pathogenesis of EGS but that a combination
of risk factors triggers the production of C.
botulinum type C neurotoxins by bacteria
present within the gastrointestinal tract.
Veterinary surgeon
Emma Houghton
XLEquine practice
Endell Equine Hospital
Equine
grass
sickness
Risk Factors
●
Grazing at pasture
●
Recent movement to a new yard or changed field within the previous 2 weeks
●
Change of feed type within the previous 2 weeks
●
Previous occurrence of cases at yard
●
Increased soil nitrogen content, pasture disturbance or higher herbage within pastures,
in particular Ronunculus species (buttercups)
●
Age: peak incidence in 2-7 year old horses
●
Good body condition score
●
Use of an ivermectin anthelmintic
●
Weather: cooler, drier weather and irregular ground frosts
Increased risk of disease has been shown with:
Figure 2: Ptosis (drooping) of both left and
right upper eyelids
Figure 1: Dysphagia with food and saliva
emerging from both nostrils