Horse owners, yard managers and those responsible for horses are being urged to remain vigilant following a recent increase in reported cases of Equine Grass Sickness (EGS).
The Equine Infectious Disease Surveillance (EIDS) team is highlighting the importance of monitoring for cases and keeping up to date with available risk information, working alongside the Equine Grass Sickness Fund (EGSF).
What causes Equine Grass Sickness and what should owners look for?
The exact cause of Equine Grass Sickness (EGS) remains unknown, although the damage it causes to the nervous system suggests that a toxin may be involved, with current research investigating several possible causes. The disease primarily affects horses with access to grazing and is particularly associated with spring and early summer. Signs can vary depending on whether the disease is acute, subacute or chronic, but may include difficulty swallowing, reduced appetite, colic, reduced gut sounds or faecal output, sweating, muscle tremors, drooping eyelids and rapid or severe weight loss. Acute cases can develop very quickly and may involve severe gut paralysis and gastric reflux.
A number of factors have been associated with increased risk, although these do not mean that a horse will necessarily develop the disease. Risk factors include being a young adult horse, recently moving onto a premises, grazing on land where previous cases have occurred, and periods of cool, dry weather. Research has also identified potential links with pasture and soil management, including soil disturbance, close grazing and poaching. The EGSF recommends considering measures such as minimising soil disturbance and exposure, avoiding sudden dietary changes, reducing exposure to fields with a previous history of EGS and, where appropriate, providing supplementary forage such as hay or haylage. These measures may help reduce risk, but there is currently no guaranteed way to prevent EGS because its underlying cause has not yet been established.
Why might cases still be occurring as we move into autumn?
Although Equine Grass Sickness is most commonly associated with spring and early summer, cases can occur later in the year, so vigilance should not stop as summer comes to an end. The reasons for this are not fully understood because the underlying cause of EGS remains unknown. Research has identified associations with particular weather and environmental conditions, including periods of cool, dry weather, as well as factors relating to grazing, soil and pasture management. Conditions on individual premises can also vary considerably, meaning that the risk does not simply disappear when temperatures begin to fall. For this reason, horse owners and yard managers should continue to monitor current EGS alerts and remain aware of any history of grass sickness on their grazing.
It is also important to remember that reported cases may not necessarily reflect exactly when exposure occurred. The development and recognition of clinical signs can vary between cases, and reporting patterns can influence the number of cases appearing in surveillance data at any particular time. With the EIDS currently highlighting an increase in reported cases, maintaining vigilance through the autumn remains sensible, particularly on premises with a previous history of EGS.
What can horse owners do?
With increased vigilance currently advised, owners and those managing horses can take several practical steps.
Stay informed
Keep an eye on the latest information from the International Collating Centre, EIDS and the Equine Grass Sickness Fund, as well as the EGS case dashboard and risk information for your area.
The EGSF also operates a weather risk alert system, developed from research into weather patterns associated with increased EGS incidence. Horse owners can sign up for location-specific alerts via WhatsApp.
Take extra care where there is a history of EGS
If your yard or grazing has previously been associated with grass sickness, heightened precautions may be appropriate.
The EGSF provides guidance on management practices that may help reduce potential risk, although there is currently no guaranteed method of preventing the disease because its cause remains unknown.
Report suspected or confirmed cases
Reporting cases is extremely important to ongoing research.
The Equine Grass Sickness Fund maintains a national case reporting system, allowing information to be collected and analysed to improve understanding of the disease and its distribution. Reports can be submitted by horse owners or veterinary surgeons.
The EGSF also operates a Biobank, which collects biological samples alongside case information for research. Samples can be used by scientists investigating the causes and risk factors associated with grass sickness.
Why reporting matters
Grass sickness remains one of the most significant causes of mortality in horses in Britain. The cause has remained elusive despite extensive research, making accurate information from cases across the country particularly valuable.
The EGSF states that without case data, research cannot progress. Building a comprehensive dataset allows researchers to investigate patterns, potential risk factors and possible causes, helping to inform future prevention and treatment.
What should yard owners do?
For livery yard owners and managers, this is a useful opportunity to review your current procedures and make sure everyone responsible for horses knows where to find the latest information.
Consider:
- Monitoring current EGS alerts and risk information.
- Reviewing any previous history of grass sickness on your premises or grazing.
- Making sure staff and liveries know what signs to look out for.
- Discussing concerns promptly with your vet.
- Reporting suspected or confirmed cases.
- Considering whether any available risk-reduction measures are appropriate for your particular premises.
Vigilance doesn’t mean panic. EGS remains a complex disease, and the current evidence does not allow individual cases to be predicted with certainty. However, staying informed, recognising potential concerns and contributing information when cases occur can all help support both horse welfare and ongoing research.
Find out more
The Equine Grass Sickness Fund provides information on clinical signs, management, potential risk-reduction practices, case reporting, the EGS dashboard and its weather risk alert system.
If you have concerns about a horse showing possible signs of grass sickness, contact your veterinary surgeon promptly.