Equine grass sickness: Scots research raises hopes of breakthrough

The military camp at Monteith in 1907 was the first recognised scene of a devastating outbreak of a killer illness that left horses writhing in pain and facing almost certain death.

Now, almost 120 years since events at Barry Camp, pioneering Scottish-led research aided by remarkable modern technology is edging to within touching distance of unravelling the perplexing mystery of equine grass disease.

A string of new research projects at locations dotted around the country - spanning soil analysis to weather conditions and the use of AI technology - have raised hopes that the riddle may soon be solved.

One element of research involves the astonishing laboratory creation of a miniature version of a horse’s gut. Developed using skin cells to replicate the real thing, the lab model can eventually be used to test toxins that might be linked to the disease, and the effectiveness of therapies and even potential vaccines.

Another thread of the research has focused on weather patterns and an early warning system – potentially available to horse owners via an app – to raise awareness of weather conditions recognised as having links to equine grass disease incidents.

Elsewhere researchers are combing through dozens of biological samples taken from horses and ponies affected by the disease, hoping to find clues as to why the dreaded condition affects some but not others.

It’s thought a fatal combination of hot, dry weather followed by heavy rain, soil conditions and feed might spark a deadly chain of events leading to affected horses’ nervous systems coming under attack.

Some research has suggested the highly neurotoxic bacterium Clostridium botulinum type C, one of many microorganisms that make up a normal gastrointestinal tract, is involved.

While in a healthy horse it is controlled, a combination of other factors may trigger it to over-produce, eventually paralysing the digestive system and leaving the horse unable to eat, drink or swallow.

Acute and subacute cases are impossible to treat – equine grass sickness kills one in 200 horses in the UK every year.

A handful of chronic cases can be nursed and make a recovery, but the impact is said to leave lingering problems with digestion and even plunging some horses into ‘depression’.

For owners, the heartache of seeing a healthy horse, pony or donkey deteriorate rapidly is accompanied by the dread that others sharing fields and stables may also fall victim.

The research is being led by animal health specialists at the Moredun Research Institute in Edinburgh and is boosted by the recent establishment of the first nationwide biobank. It has gathered more than 1500 biological and environmental samples linked to horses affected by the disease.

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The biobank, supported by the British Horse Society and Equine Grass Sickness Fund, includes samples taken from three Highland Ponies owned by the late Queen at Balmoral which all died of the sickness in June 2017.

The losses of a two-year-old filly called Friendly, her mother Clunie and a male called Omar were followed less than a year later by the deaths of two prized stallions, Hercules and Lord.

As well as revealing a mass of information about stricken horses, weather conditions and feeding habits, the biobank has revealed cases of equine grass sickness, once thought to be largely a north east of Scotland problem, are more widespread than previously thought.

The research has also uncovered cases in Italy and South America.

Dr Beth Wells, EGS Project Lead, Moredun Research Institute, said: “Science is slow and getting funding is so difficult, but we are much more optimistic now because we have a big network on same project a lot of people engaged a lot helping us it’s gathering pace. 

“Around one to two percent of the UK horse population will get grass sickness and 80% of them will be dead by the end of it – that’s the devastating part.

“If it’s a family pony, it is particularly hard. This year we had one case of a little girl who had issues at school and relied heavily on her pony. One day it was alive and dead the next – that is horrible.

“It is really difficult for families as they have no preparation. It comes hard and fast.”

Equine grass sickness was first recognised following the mysterious deaths of horses at the military camp in Angus.

It then spread rapidly throughout Perthshire and into Aberdeenshire, with so many cases that politicians began to refer to it as a national crisis.

Young Clydesdales seemed particularly badly hit – the working horse population of the early 20th century was crushed by the disease which left many hundreds of horses dead every year.

Theories surrounding its causes have ranged from poisonous plants to insect bites and viruses.

Although some horses and ponies with the ‘chronic’ version can be nursed back to health, even the best care can’t save those struck with acute and sub-acute sickness.

Thoroughbred Dubai Millennium was considered to be the greatest racehorse in the world before a leg break led to the stallion being put to stud, only to die from grass sickness at the age of five despite three operations.

A crucible event in Edinburgh last year which gathered scientists, vets and horse owners with people from a diverse range of backgrounds to establish the best routes forward for research is said to have brought fresh focus to solving the riddle.

While work on weather patterns is underway at Edinburgh University, a joint project between Moredun Institute and the James Hutton Institute in Aberdeen aims to compare what’s in soil from a hot spot of cases in Aberdeenshire with biological samples from actual cases.

Processing of the samples at the Hutton has had initial support thanks to a £4,000 donation from Aberdeenshire business owner Emily Anderson, whose sister, Scottish Champion dressage winner Gillian Green’s warmblood horse Jed is one of the few to survive the disease.

“It was a horrific experience to see Jed stuck with the chronic form of this terrible disease,” said Gillian, who as manager of the National Soils Archive at the Hutton is in charge of processing the samples.

“He survived, thanks to a lot of support and effort from Emily, the stables and the wider community, but most don’t.

Gillian Green and her horse, Jed, which survived equine grass sickness (Image: James Hutton Institute)

“By matching the soil samples with biological samples from horses that have contracted EGS, we hope modern techniques like environmental DNA (eDNA) could help to finally pinpoint the cause of this nightmare disease – or rule it out.”

Meanwhile, the use of artificial intelligence at the University of Surrey to sift through mountains of data surrounding toxins, biological and environmental samples has been described as a ‘gamechanger’ by Dr Wells.

She added: “The best information we have is that it’s a neurotoxin that attacks the nerve cell.

“We have leads, we know where we are looking. We have databases of bacteria and fungi that can produce neurotoxins that can produce this amount of damage, and there might be one out there that we don’t know about.

“The difficulty we have is weather, soil, pasture and the horse, and then all the things that owners do randomly which are fairly variable.

“Immunity is a big gap in our knowledge: why do some horses go down with it and others don’t when they’re in the same field eating the same things in the same weather?”

Key to it all, she added, is the horse itself – making the search for answer heavily reliant on, sadly, more horses succumbing, and their samples being added to the biobank.

“We can’t replicate this disease in an experimental trial, we have to use field cases,” she said.

“Unfortunately, it relies on us getting these samples from horse owners.”