New research on equine grass sickness (EGS), published as a free special collection in the Equine Veterinary Journal (EVJ) this month, has helped to improve veterinarians’ and researchers’ understanding of this devastating disease.

Four separate studies are included, reporting novel risk factors for the disease, identifying key differences between EGS and botulism (questioning the hypothesis that EGS is caused by neurotoxins from Clostridium botulinum), reporting a novel diagnostic technique, and showing the value of monitoring weight loss to help predict whether individual horses with chronic EGS are likely to survive.

Despite more than 100 years of research, supported predominantly by Moredun Foundation Equine Grass Sickness Fund, the cause of EGS remains unknown. Since it almost exclusively affects grazing horses, a pasture-derived neurotoxin has been implicated.

The disease causes gut paralysis resulting from damage to parts of the nervous system that control involuntary functions. The acute and subacute forms of EGS are invariably fatal, while around 55% of chronic cases can survive and return to a useful working life. The United Kingdom has the highest incidence of EGS in the world—it is estimated that the disease kills 1 to 2% of horses in the United Kingdom annually. Cases are more common in spring.

In terms of risk factors, the study “Equine grass sickness in Scotland: A case-control study of environmental geochemical risk factors” suggests that the high inciden