What is "grass sickness"?

[Sondra]

I recently read about the death of a horse from "grass sickness." I did not want to intrude into the conversation by asking what this is, but I don't want my horse to suffer from my ignorance of this illness.
Would someone please enlighten me with the details? Forewarned is forearmed!

[Drummers mum]

Sorry, don't know much other than I think its quite rare and its just a deterioration in health. Mainly posted as I would like to know more too!

[Portia]

Here's the first part...


The website is www.grasssickness.org.uk.



Grass Sickness is a disease of horses, ponies and donkeys in which there is damage to parts of the nervous system which control involuntary functions, producing the main symptom of gut paralysis. The cause is unknown but the nature of the damage to the nervous system suggests that a type of toxin is involved. The disease occurs almost exclusively in horses with access to grass.

The disease was first recognised about 1907 following an outbreak in army remount horses near Dundee. The incidence increased markedly and at least in Scotland, hundreds of horses, mainly draught animals, died annually from grass sickness in the 1920’s. It is said that the losses were so severe that the introduction of tractors was artificially accelerated as a result. In the 21st century, grass sickness continues to kill horses of all breeds and it has been estimated that approximately 1 in 200 die annually from the disease in some parts of the UK.

DISTRIBUTION

Great Britain has the highest incidence of grass sickness in the world and the disease occurs in most areas of England, Wales and Scotland. It is a significant problem in many areas of Great Britain, with eastern counties being particularly at risk. The disease is well recognised in northern Europe, especially Sweden, Denmark and Germany, with fewer cases in France, Belgium, Italy, Holland, Norway, Finland and Switzerland. Two cases have been identified in Ireland, and two in North America.

SPECIES, BREED AND SEX

Grass sickness affects horses, ponies and donkeys, and there have even been cases in a captive zebra and a Przewalski’s horse. It used to be thought that Clydesdales were more susceptible and that Shetland ponies and thoroughbreds were resistant but this has been disproved and the incidence in different breeds reflects their numbers in the general population in the worst affected areas of the country. Mares may be at slightly less risk than stallions and geldings but this is still under investigation.

AGE

Grass sickness occurs in all ages from 4 months to over 20 years but the greatest number of cases occurs in 2 to 7 year olds with a peak at 3 to 4 years. The reason for the age distribution is uncertain although young foals presumably are not affected because they are not consuming sufficient herbage with which the disease is associated. The lower incidence in older horses, and surviving horses in a group in which a case has occurred suggest that animals exposed to the causative agent may develop a degree of resistance to the disease.

SEASON

Cases occur in every month of the year but most are seen between April and July with a peak in May. In some years, a second, smaller peak occurs in the autumn or winter. At least in Scotland, the lowest incidence is in August which may be a weather-associated effect (see below).

FEEDING

Grass sickness, as its name suggests, is strongly associated with grazing but there have been a few cases in animals with no access to pasture. In these rare cases, hay has been implicated as the source of the causal agent. Although most cases have been at grass full-time or during the day, the disease can affect horses which have only a few minutes’ access to grass daily. There is no association with type of pasture (new ley, permanent pasture, hill grazing, clean or ‘horse-sick’ pasture) nor with fertilisation. However, a recent suggestion that grass sickness is more often seen in pastures with a high clover content is under investigation. Giving supplementary feeding in the form of concentrates does not have a protective effect, but hay feeding reduced the risk factor in one study.

PREMISES

It is well recognised that certain premises, or even fields within single premises are associated with the occurrence of grass sickness cases. The reason for this is unknown and much effort has gone into comparing ‘good’ and ‘bad’ fields especially with respect to the plant and fungal species present (see below). Animals which have been on an affected premises for less than 2 months are more likely to develop the disease. Commonly, only one animal is affected at a time but ‘outbreaks’ of the disease with several cases in a period of a few weeks are not infrequent.

PREDISPOSING FACTORS

Stress appears to be a factor in predisposing to the disease and a significant number of animals have a history of recent stress including recent purchase, mixing with strange horses, travelling a long distance, breaking and castration. Animals in good to fat condition also appear to be predisposed.

Many horse owners have firm opinions about the type of weather prevailing when grass sickness cases occur. In a survey of weather conditions in the two weeks preceding multiple-case outbreaks, it was found that cool, dry weather with a temperature between 7 and 11°C was recorded in a statistically significant number of instances. This may partly explain the higher incidence of the disease in the eastern side of Britain where such conditions are more prevalent.

Results of a recent survey suggest that the risk of developing grass sickness is slightly higher in horses which are wormed more frequently. However, it should be emphasised that the consequences of not worming can be very serious or even fatal and it is not suggested that owners should decrease their use of wormers. There is also no indication that wormers themselves contain the toxin that causes grass sickness. Other risk factors include increased numbers of horses on the pasture, mechanical droppings removal, soil disturbance, harrowing, and presence of birds on fields.

CAUSAL AGENT

The cause of grass sickness is unknown despite almost 100 years of investigation. Many potential causes have been examined over the years including poisonous plants, chemicals, bacteria, viruses, insects and metabolic upsets. A common suggestion by horse owners is that mineral or vitamin deficiencies may be the cause. None have any proven link with the disease, although selenium deficiency, which results in reduced levels of protective antioxidants in the body, may have some role to play. Grass sickness does not appear to be contagious and the type of damage to the nervous system suggests that a toxic substance is likely to be involved. A current theory under investigation is the possible involvement of Clostridium botulinum, a soil-associated bacterium. Work is also underway on the cyanide-producing properties of white clover although any link with the disease is not yet proven.

CLINICAL SIGNS

Grass sickness occurs in three main forms, acute, subacute and chronic, but there is considerable overlap in the symptoms seen in the three forms. The major symptoms relate to partial or complete paralysis of the digestive tract from the oesophagus (gullet) downwards. In acute grass sickness, the symptoms are severe, appear suddenly and the horse will die or require to be put down within two days of the onset. Severe gut paralysis leads to signs of colic including rolling, pawing at the ground and looking at the flanks, difficulty in swallowing and drooling of saliva. The stomach may become grossly distended with foul-smelling fluid which may start to pour down the nose. Further down the gut, constipation occurs. If any dung is passed, the pellets are small, hard and may show a ‘cheesy’ coating of mucus. Fine muscle tremors and patchy sweating may occur. In this form, the disease is fatal and the horse should be put down once the diagnosis is made.

In subacute grass sickness, the symptoms are similar to those of the acute disease but are less severe. Accumulation of fluid in the stomach may not occur but the horse is likely to show difficulty swallowing, mild to moderate colic, sweating, muscle tremors and rapid weight loss. Small amounts of food may still be consumed. Such cases may die or require to be put down within a week.

In chronic grass sickness, the symptoms come on more slowly and only some cases show mild, intermittent colic. The appetite is likely to be reduced and there will be varying degrees of difficulty in swallowing but salivation, accumulation of fluid in the stomach and severe constipation are not a feature. One of the major symptoms is rapid and severe weight loss which may lead to emaciation. Previously, it was thought that nearly all such cases died and that the few which survived made only a partial recovery and were subsequently useless for work. This is now known to be incorrect (see section on treatment).

[Portia]

and here's the second!

DIAGNOSIS

The symptoms described above may seem quite clear-cut but unfortunately not all affected animals show all these signs and it can sometimes be very difficult for the veterinary surgeon to distinguish grass sickness from other causes of colic, difficulty in swallowing and weight loss. This is compounded by the fact that there is no non-invasive test for diagnosing the disease in the live animal although certain blood tests (haptoglobin, cortisol and catecholamines) and examination of peritoneal fluid can be helpful, when considered together with the symptoms. A definite diagnosis can be made only by microscopic examination of nerve ganglia after death or by surgical removal of a piece of small intestine by opening the abdomen. Characteristic degenerative changes in the nerve cells can then be demonstrated in the tissues. However, a recent test involving application of 0.05% phenylephrine eye drops, which reverses the drooping eyelids seen in grass sickness, has potential as a test for use in the live horse.




TREATMENT

As previously stated, treatment should not be considered in acute and subacute cases. However, in chronic cases, if the animals are not in much pain, can still eat at least a small amount and are still interested in life, treatment of chronic cases can be attempted. The correct selection of potentially treatable cases using these criteria requires experience but is essential. Not all chronic cases are treatable. The management of selected cases has been the subject of study by the Grass Sickness Research Team since 1989 and the results have challenged the view that chronic cases either die or at best only partly recover. Treatment of chronic cases involves provision of palatable, easily swallowed food e.g. chopped vegetables, grass and high energy concentrates soaked in molasses. It is essential that high energy foods are consumed as chronic cases fed roughages and succulents alone will invariably die. Nursing is also vital and provides the mainstay of management. The patients require constant stimulation by human contact, frequent grooming to prevent them becoming scurfy and sticky with sweat and, in some cases, rugging which has been found to reduce sweating and prevent hypothermia. Appetite stimulants may also help. By careful attention to the management regime we have developed, the recent recovery rate for carefully selected cases in the R(D)SVS Large Animal Hospital is now approximately 70% and veterinary practitioners in the field are now reporting success when following the same regime. Contrary to commonly held views, a follow-up study has shown that 41% of these recovered cases were back to work including hunting, racing, eventing, 33% were being hacked, preparing for competitive work or being used for breeding and the other 26% (the more recent cases) were still gaining weight and recovering at the time of the survey. None of the survivors were described as being of no use. This represents a major improvement in the prognosis for such cases compared with the situation before the late 1980s.
Grass sickness occurs in three main forms, acute, subacute and chronic, but there is considerable overlap in the symptoms seen in the three forms. The major symptoms relate to partial or complete paralysis of the digestive tract from the oesophagus (gullet) downwards. In acute grass sickness, the symptoms are severe, appear suddenly and the horse will die or require to be put down within two days of the onset. Severe gut paralysis leads to signs of colic including rolling, pawing at the ground and looking at the flanks, difficulty in swallowing and drooling of saliva. The stomach may become grossly distended with foul-smelling fluid which may start to pour down the nose. Further down the gut, constipation occurs. If any dung is passed, the pellets are small, hard and may show a ‘cheesy’ coating of mucus. Fine muscle tremors and patchy sweating may occur. In this form, the disease is fatal and the horse should be put down once the diagnosis is made.

In subacute grass sickness, the symptoms are similar to those of the acute disease but are less severe. Accumulation of fluid in the stomach may not occur but the horse is likely to show difficulty swallowing, mild to moderate colic, sweating, muscle tremors and rapid weight loss. Small amounts of food may still be consumed. Such cases may die or require to be put down within a week.

In chronic grass sickness, the symptoms come on more slowly and only some cases show mild, intermittent colic. The appetite is likely to be reduced and there will be varying degrees of difficulty in swallowing but salivation, accumulation of fluid in the stomach and severe constipation are not a feature. One of the major symptoms is rapid and severe weight loss which may lead to emaciation. Previously, it was thought that nearly all such cases died and that the few which survived made only a partial recovery and were subsequently useless for work. This is now known to be incorrect (see section on treatment).

[Portia]

and finally...

CURRENT RESEARCH

The Grass Sickness Research Team, and others are currently undertaking several lines of investigation. The main lines of investigation at present are the role of Clostridium botulinum type C and cyanide-producing clover as predisposing or causal factors. It has been discovered that the concentration of C.botulinum type C toxin is high in the intestine of acute cases and that horses with low levels of antibody to the bacteria and its toxin are at increased risk from the disease.

SUPPORTING GRASS SICKNESS RESEARCH

The Equine Grass Sickness Fund is the only registered charity in the UK raising funds specifically for research into grass sickness. EGSF is dedicated to supporting and advancing research into grass sickness and further improving the treatment of chronic cases.

If you would like to know more about supporting grass sickness research or make a donation, please contact Joyce McIntosh, Secretary, Equine Grass Sickness Fund, The Moredun Foundation, Pentlands Science Park, Bush Loan, Penicuik, Midlothian, EH26 0PZ.

Tel: 0131 445 6257 Fax: 0131 445 6235 Email: equine@mf.mri.sari.ac.uk

Website: www.grasssickness.org.uk

(Produced by the Equine Grass Sickness Fund 23/10/02)


A good friend lost her beloved boy to this condition some two years back.
The rapid onset of acute grass sickness is quite simply shocking, and my heart goes out to those who have suffered it. For those interested, donations can be made to the society. - Portia

[Drummers mum]

Wow! :(

[Portia]

Sorry, didnt have the time to summarise :o

[LindaAd]

I'll summarise, Portia, although it's worth going back and reading all the detailed information that you've posted.

It's a horrible wasting disease that destroys horses really fast, by working on their nervous system: they can't eat, and they just get thinner and weaker and die within a few days. There's no cure and no real treatment; occasionally a horse survives, but that's really rare.

That's the acute form of the disease; there's also a subacute form, which is different.

No one really knows what causes it, although there's a lot of research been done, and is still going on - Portia's posted a lot of details.

It's heartbreaking, because it affects younger horses most often, I think the age is around 4 - 6. My instructor lost her beautiful, homebred 5 year-old mare to grass sickness.

That's the summary. Now you can go and read more about it.

Linda

[laz]

My Dales died of it. I rode her in the morning and later that nite she was dead that shows you how fast the acute form is. The symtoms she had at night time were like colic, but she couldnt swallow food or do the toilet, she kept wanting to lie down. She had to be taking to the vet hospital in Edinburgh for a proper diagnosis but died during this i didnt even get a chance to say goodbye. :(

[horsey1]

Really sorry to hear that Laz, a horse at my last yard also died last year of it its a horrible thing to see, hers also went to the Bush but had to be pts :( she was only 7 and beautiful

[Sondra]

Thank you all for the information, and please accept my deepest sympathy for the loss of your beautiful horse.
I have learned more from reading these post's than I have from any of the books I have read.
Thank you for sharing

[amandal]

Thanks from me too, my yard's lost 2 horses from it in the last few weeks, one yesterday and one just before Bank Holiday. I've been reading up as much as I can but that's very clear and unscientific so easily understandable.

[Portia]

Glad to be of help, and I'm so very sorry to hear of other's loss.
My friends' experience was very similar to yours Laz, just so very very fast. The only positive aspect was that her much loved boy didnt suffer too long.