By vet Freya Wood
Equine Grass Sickness has been a topic of conversation in the local news recently, but cases were first reported in Scotland in 1907.
Great Britain currently sees an estimated 1 in 200 equines dying from the disease yearly - the highest incidence of grass sickness globally - with cases seen across GB but more often in the east.
Disease mostly occurs between April to July with a peak in May. Historically the east of Scotland had large numbers of cases and much of the research into Equine Grass Sickness has been performed between the Royal (Dick) School of Veterinary Studies (R(D)SVS) and the Moredun Research Institute, both in Edinburgh.
Equine Grass Sickness affects the parts of the nervous system associated with the automatic functions of the body which in the course of disease mostly presents as gut paralysis. The disease presents in three forms: acute, subacute and chronic. Horses do not move between the forms as these describe the severity and type of clinical signs they exhibit. Diagnosis is predominantly based on clinical signs, with a definitive diagnosis only able to be made on samples collected at either exploratory abdominal surgery or at post-mortem.
The acute form of the disease is the most severe. Affected equines become very unwell very quickly and either die or are euthanased on welfare grounds within two days of disease onset. These horses often show severe colic signs due to severe gut paralysis, with the stomach becoming full of foul-smelling fluid which discharges down the nostrils. They may also have patchy sweating, muscle tremors, be drooling saliva and unable to swallow. Subacute disease presents similarly but less severe but horses die or are euthanased on welfare grounds within a week. They show mild to moderate colic signs, patchy sweating and muscle tremors as well as also having rapid weight loss.
The chronic presentation is the least severe with the biggest sign being severe weight loss. Cases may also show mild colic signs, muscle tremors and patchy sweating. This disease form can be nursed back to health, and despite commonly held beliefs, can return to ridden work. There are recovered cases returning to racing, hunting and eventing and in data collected about recovered cases, all returned to a use of some type which is a huge step forward as this has not always been the case.
Greatest recovery success rates have come from hospital cases treated at R(D)SVS Equine Hospital, who have led the way with developing treatment regimens, with a 70% recovery rate now being reported. Treatment is hard work, requiring careful management and nursing care, and a focus on providing high energy feeds. Similar success is also being reported by vets outside of a hospital setting when following the same treatment regimens which is encouraging.
Equine Grass Sickness is not thought to be contagious. However the cause still remains unknown making prevention advice challenging. There are currently a number of hypotheses and research is ongoing. Equines between the ages of 2-7 years of age are more likely to be affected, however disease can be seen at any age. Almost all cases have had access to grass, with stress affecting the gut microbiome (including changes to diet, recent travel or change in premises or routine), weather patterns (prolonged drought followed by heavy rainfall), and recent ground disturbance all implicated as risk factors. Currently it is advised to minimise exposure to pasture where previous cases have occurred or to supplement forage if these areas cannot be avoided. It is also advised to avoid pasture disturbance such as harrowing, mechanical dung removal, construction work and pipe laying, as well as preventing ground becoming poached.
The Equine Grass Sickness Fund has a wealth of information on their website which is run by those involved in research