FOR more than 100 years, the fear of equine grass sickness (EGS) has haunted Scottish horse owners. No-one has known the cause, no-one could prevent it, and no-one knew how to treat it. On the east coast of Scotland in particular, the risk of equine grass sickness is always dangerously close.

But now researchers believe that a Scottish study will bring them much closer to understanding the disease for the first time, and at the same time, they hope they will soon be able to introduce a vaccination programme which will protect horses from it.

EGS is almost always fatal. Horses may at first appear to have the signs of mild colic, or choke, but in fact their nervous system has been attacked, causing paralysis of the gut. Horses may also show patchy sweating, a racing heart beat, and drooping eyelids. In the acute or sub-acute forms, death will come in a couple of days. Horses with chronic EGS will waste quickly over a period of weeks. Only a very few survive.

EGS was first recorded in Angus in 1909. It spread quickly, becoming established in Perthshire, Kincardine, Aberdeenshire and Moray. These areas remain hotspots for EGS, although cases can be found anywhere in the country.

Thousands of working Clydesdales died in the first half of the 20th century, despite extensive field and laboratory trials. One theory, which was popular in the 1920s, was that grass sickness was connected to botulism. An Aberdeen scientist Dr JF Tocher carried out vaccination trials in the 1920s, and claimed that his 'serum' could give significant protection to horses at risk.

The botulism theory vanished from the scientific debate when Tocher was discredited. But in recent years, researchers have shown a renewed interest in the link with botulism.

Vets now believe that the most likely cause of grass sickness is a bacterium called Clostridium botulinum type C, which is commonly found in soil. It can produce a number of toxins including a powerful neuro-toxin to which horses are particularly sensitive.

They believe that horses ingest the bacterium while they are grazing. A combination of risk factors then triggers the bacterium to produce the neuro-toxin in the horse's intestine.

The family of clostridial diseases has been recognised for many decades. Sheep and cattle are routinely injected for up to 10 different clostridial illnesses, while horse owners already vaccinate for one clostridial disease – tetanus.

This knowledge, along with evidence that horses can develop natural immunity to EGS with exposure to the bacterium, suggests that it should be possible to prevent EGS by vaccination.

Now a number of vets and yards in Aberdeenshire and Perthshire are involved in piloting a vaccine trial against C botulinum type C. One hundred horses and ponies are enrolled in the current research. It is hoped to extend the trial to a full nationwide study later in the year.

Dr Jo Ireland is co-ordinating the research on behalf of the Animal Health Trust in Newmarket, and the Royal (Dick) Vet School in Edinburgh. She's been surprised by the enthusiasm of owners to take part.

"There's been an overwhelmingly positive response. Everyone involved has some experience of grass sickness, and they are keen to do what they can to help prevent it," she said.

The horses and ponies on the trial all come from yards which have experienced EGS in the last three years. On each premises, half the animals are being given the vaccine, and half are being injected with a harmless placebo.

Donview Vets in Inverurie, Aberdeenshire have recruited almost half the horses in the study. The local vets give the trial injections, take blood tests and carry out heath checks, reporting back to Dr Ireland. But vet Laurie-Anne Ferguson, who has done a lot of the work, says she doesn't know which horses are getting the vaccine.

"We are supplied with two bottles, one marked A, and the other labelled 1, so I have no way of knowing which horse or pony is getting the vaccine," said Laurie-Anne.

Dr Ireland explains that this is important for the scientific validity of the trial: "This process is called 'blinding' and it means that none of the observations or trial findings can be influenced by the expectations of those involved."

Just outside Inverurie, The Cabin Equestrian Centre has seven horses and ponies taking part.

Owner Fiona Quennell says she is delighted to be able to help with such important research. She has lost three horses in 19 years on a farm where there are always more than 30 horses. She is convinced that each case coincided with soil disturbance and ground works at the centre.

She admits that EGS is her worst nightmare. "When it happens, you look at them, and you are just praying it's not grass sickness, even when you know in your heart that it is," said Fiona.

In the most dramatic case she has experienced, a six-year-old Irish mare was in perfect health at noon, and was spotted exhibiting all the symptoms of EGS by 2pm. Two hours later, the horse was dead.

"She was a lovely mare. It was shocking and heartbreaking to see how quickly she went from being fit and healthy to having no hope at all," she says.

So far, the animals in the pilot trial have all had three injections, similar to starting any vaccination course, and they will get a further booster in May.

The current pilot has been designed as the fore-runner of a full vaccine trial. Its purpose is largely to act as a feasibility study, testing the practicalities of the reporting system and vet checks.

The owners have to keep a detailed health record for each horse for a week after every injection.

This includes whether the horse has any heat or swelling at the injection site, and whether it has any change in behaviour or appetite.

The vets take blood samples which are returned to the Animal Health Trust to check antibody levels to assess how the horse's immune system is responding to the vaccination.

It is hoped that the full study, involving a thousand animals, will begin later this year, if funding can be secured. The research will be nationwide, but Scottish hot-spots will still be at the heart of the study.

If the trial is successful, Dr Ireland hopes the vaccination could be available within a couple of years. Although the licensing procedure is notoriously slow, it may be possible to push for a relaxation of the rules.

"If there are no other licensed treatments available, you can request special consideration so the drug can be prescribed before the full marketing authorisation comes through. If the full trial proves successful, we would hope that might be possible in this case," added Dr Ireland.

Scottish horse owners will be crossing their fingers that the current research will finally bring the answers they have been hoping for. After such a long and unhappy association with EGS, it would be a fitting outcome if the breakthrough was at last found in Scotland.

If you would like to contribute to the research, or know more about EGS, go to www.grasssickness.org.uk