The nightmare of Equine Grass Sickness

What can you do to minimise the risk factors?

SNE has been finding out

Many of you will have known the nightmare of losing a horse or pony to equine grass sickness (EGS) and will probably be dreading this particular time of year when grass sickness is most likely to strike. There are other horse owners who are still unaware of what grass sickness is, what the symptoms are and what can be done to minimise the risk of an animal developing this normally fatal disease.

The disease was first recognized in about 1907 following an outbreak in army remount horses near Dundee and since then the incidence of grass sickness has spread across Britain, particularly in Scotland and continues to kill horses of all breeds today. It is estimated that, in some areas, 1 in 200 animals die of the disease annually.

There are three categories of grass sickness – acute, sub-acute and chronic (see panel for the symptoms of each). Only in the chronic category will a horse or pony have a chance of recovery. In acute cases, death can occur within hours of symptoms being displayed.

Equine Grass Sickness has been a research interest of the Moredun Institute for many decades and an active Grass Sickness Research Team involving collaboration between the Moredun, Royal (Dick) School of Veterinary Studies and other institutes has been in existence since 1986.

In the past, Prof Ian Poxton (Medical Microbiology, University of Edinburgh) and colleagues have concentrated on the association with EGS of Clostridium botulinum, a type of  highly neurotoxic bacterium. Another important research topic is what triggers EGS in some horses and not others, even when they are grazing together.

And so, while the scientists work on to find what causes the disease and to develop a vaccine against it, what can the horse owner do to minimize the risk of their animals developing grass sickness?

One horse owner, Catriona Rowan, from Perthshire, has lost 8 horses to grass sickness over a period of 35 years and has done a lot of her own thoughtful research into how best she can manage her horses to prevent losing any more animals to this vile disease.

Catriona focuses on maintaining a healthy gastro-intestinal tract by maximizing gut flora health.She also states that you should always have a good tub lick available with a broad spectrum of minerals all year round. Many of the identified increased risk factors for EGS involve a change in the horse’s circumstances

Stress Factors the horse owner can manage

·         Change of diet and worming

• Change of social companions.
• Change of grazing or stabling.
• Change of routine (including attending shows and events).
• Medication for any reason, particularly antibiotics, as they will affect the gut bacteria in most cases.

Stress factors outwith owner’s control

• Growth - 80% of EGS cases are 2-7 years old so this should be the main period of vigilance.
• Changing of coat in spring and autumn
• Coming into season for mares
• Adverse or extreme weather changes causing a check or flush in grass growth rates, the majority of which occur in spring and autumn when late or early frosts and sudden weather changes are most likely. Most cases of EGS occur in April or May with another peak in September/October during some years. These weather events can cause rapid and significant changes in the mineral, fructan and carbohydrate content of the grass

How the horse owner can minimize risk

All of the above changes could cause unseen stress in the horse which might affect the gut flora. If at all possible, avoid multiple changes.

Example: You acquire a new horse. You move him to your yard, feed him to his previous owner’s schedule and take a dung sample to send for a worm count.

Over these first days a pre/probiotic supplement can be introduced to be fed for the first 2 weeks or so. During the second week you could begin to introduce your own feed and routine.

After that, new companions can be put into his field (mildest mannered first to reduce bullying). Should the worm count indicate that worming is necessary try to do this during a period of mild, wet weather when the grass is likely to be stable in mineral content, ie no sudden changes in temperature are forecast.

Catriona says, “Now, when I worm my horses, I add some pre/probiotics to the feed for around 10 days following treatment and I am especially careful to ensure that they have free access to a multi-mineral lick (low in molasses) and a daily portion of pre-soaked organic seaweed*, being careful to follow manufacturers’ instructions. A handful of grain can be added for palatability and fed most days during the grass growing season as that is when these variations in fodder quality can occur. The same would apply if your horse had to have veterinary treatment for any reason.

“During winter, when the relatively more stable mineral content of the diet is contained in hay then it is not necessary to feed the seaweed more than once or twice a week, unless some other stress factor has been introduced into the horse’s life. Seaweed has been chosen because it contains a small amount of a vast array of different minerals, especially manganese, which is important for bone growth and to the gut flora for their nutrition. On the assumption that cut and dried forage has a more stable nutritive content than growing grass, then it would be sensible to feed hay during stress periods or to try to make significant changes to your horse’s environment whilst he is on a predominantly hay/haylage diet.

“This routine has been employed on my premises since 2001, just after I lost my most recent of the 8 cases of EGS that I have suffered over 35 years. Instead of avoiding young horses and stress, I have tried to test out my theories on feeding the gut flora in order to maintain a healthy digestive process. To be simplistic: Healthy Gut Flora = Healthy immune system = Healthy horse.

“The objective is to maintain whole gut health and integrity by thoughtful management of change and by striving to feed the all-important Gut Flora during periods of stress.”

Interesting facts: One third of a horse’s dung is composed of discarded gut bacteria; this demonstrates forcibly how important these bacteria are in the digestive system. There are more microbial cells in the human body than there are human ones so horses could well be the same – these microbial cells are vital and we should look after them! They have to be continually replenished or the digestive process grinds to a halt.

You can find more information on scientific research
into EGS at www.pubmed.nl

You can also find more information generally on EGS at www.equinegrasssickness.org.uk

Or call the Equine Grass Sickness Fund on 0131 445 6257 for help and advice