The Queen’s horses are set to help unravel the mysteries of a devastating disease

First identified in Angus in 1907 following the deaths of a number of Army horses based near Montrose, the sickness tends to strike between April and June, and is believed to claim the lives of around 150 horses, ponies and donkeys across the UK every year.

While it can occur anywhere, horses across the north of Scotland and along the east coast are thought to be particularly vulnerable. That has raised suspicions that weather and temperature may be one of its key triggers.

Genetics, gut health, stress, soil conditions, a bacterium linked to botulism, and fungus have also been suggested.

The disease affects the animal’s nervous system, sending signals which paralyse its digestive system and leaving it unable to eat or drink.

Around 95% of those affected die within a few hours. The remainder need intensive nursing and can still have shortened lives as a result.

With no current clear explanation as to why it happens, there are no guaranteed preventative measures and no cure. While owners face the difficult decision of having their animal humanely destroyed, there is additional anxiety over whether other horses which share the same field, feed and stables could also succumb.

Studies carried out at the Royal Deeside estate will feed into a range of research being led by Edinburgh’s Moredun Foundation which aims to unravel why some healthy horses are struck down while others, often sharing similar feed and environments, remain unaffected.

Earlier this month – peak time for the disease to strike - the Foundation, along with the Equine Grass Sickness Fund and supported by the British Horse Society launched the first nationwide biobank which will gather samples and information linked to horses affected by the disease.

As well as accepting post-mortem samples, it will build a database of historic cases of equine grass sickness which it’s hoped spotlight connections between cases, helping to solve the 114-year-old mystery.

Included in the work will be an attempt to recreate a petri-dish sized horse digestion system, in the form of mini-gut organoids. The mini tissues, developed from cells, can then be probed with causative agents to assess their responses. Work to gather samples from horse owners around the country has begun, while later this year a researcher at the Queen’s Balmoral estate will start creating an exhaustive record of various environmental factors to accompany non-invasive samples taken from the Highland Pony herd.

Three of The Queen’s Balmoral working ponies, a two-year-old filly called Friendly, her mother Clunie and a male called Omar, were struck down by equine grass sickness in June 2017.

The losses were followed the following May by the deaths of a further two prized stallions, Hercules and Lord.

The Queen, who names every foal born at Balmoral and takes a close interest in the stud, was present when Hercules fell ill and made a final emotional visit to see the impact of the condition and say her farewells.

While the Balmoral herd has not been affected by equine grass sickness since 2018, in recent weeks five horses have died within a three-week spell at a herd located less than 20 miles away.

Sylvia Ormiston, who manages Her Majesty's Balmoral Highland Pony Stud, said: “We are offering as much held as we can – anything we’re asked to do, we’ll do our best to make happen.

“We have the support of the Queen. She was able to be there in May 2018 and see the stallion that was affected.

“She understands how awful it is for owners to lose a horse.”

She said the new biobank and research programme had raised fresh hopes among owners that the cause of grass sickness can be found.

“This disease is so random, our first pony was in a field of five, second in a field of 11 and they were the only ones affected.

“What is frustrating is after 100 years of research we are no further forward, there’s no cure. We have to find out what causes it to prevent it in the first place.

“Hopefully now any animal that is lost, doesn’t die in vain.”

One theory is that clostridium botulinum in the soil could be at least partly to blame. Others suggest it may be linked to a fungus growing on grass which may give off a toxin under certain circumstances, lasting just a few hours at a time.

There are also suggestions that certain horses may be genetically susceptible to the sickness. The possibility of a genetic link means the Balmoral Highland Ponies are of particular interest due to the quality of the bloodline.

Mordeun Foundation research fellow, Dr Kathy Geyer, said the Balmoral herd would be followed throughout the course of a year, while other study sites have been established at farms with a historic record of equine grass sickness.

“We are taking a multi-disciplined approach, talking to soil scientists, collecting environmental samples, looking at the immune systems and why certain horses are susceptible, working with owners for sample collection and also looking at risk factors.

“It may be there is existing data which needs to be studied in a different way, with technology now available that we can use.”

Kate Thomson, administrator of the Equine Grass Sickness Foundation, said horses have been affected from Aberdeen to Wales in recent weeks, with a series of clusters involving multiple horses from a single herd.

It has raised concerns that 2021 may be a peak year for grass sickness cases.

She added: “We have had an amazing response among owners already and we want to capture as many cases as we can.

“This disease is complex, it’s like a perfect storm. You need a horse that’s susceptible, the right weather that causes it to be present and unfortunate circumstances.

“This is a joint effort involving vets, horse owners, charities across the UK and scientists working together.

“It is an awful disease that for over 100 years has completely bafflect intelligent people.

“If we can make the biobank a success, then the answers must be in there somewhere.”

Yvonne MacLean was determined not to lose her horse Malbec to equine grass sickness – even though nursing him back to health almost cost her marriage.

“We were so focused for 14 weeks on trying to get him back to health, that it took an enormous toll on both of us, emotionally and physically,” she said.

"We were exhausted and it very nearly ended our marriage."

Malbec was a healthy 17hh Hanoverian gelding when he fell ill in August 2014. Within six weeks his weight had slumped from 750kg to just 596kg.

“He wouldn’t eat, so we were syringe feeding him every hour for three weeks. We were fortunate, not many owners have the chance to do what we did.”

While Malbec survived, a neighbouring croft in Dingwall lost two horses, and a further two the following year.

Yvonne, who recently shaved her head to raise money for research into equine grass sickness, said: “As owners we have no control over this disease, we don’t know when or why it will strike and we can’t take preventative measures.

“We are in the lap of the gods.”