Atypical myopathy (AM) is a deadly equine disease that is rapidly becoming more common in the UK and Europe. Only three cases were reported in Britain in 2010 — but three years later, the figure had already climbed to 51. Similar to the Seasonal Pasture Myopathy that affects horses in the United States, AM can strike quickly, causing huge suffering as it damages muscle tissue. Sadly, it is often fatal.
Unfortunately, we know relatively little about the way the disease is contracted, but there are things you can do to keep your horse as safe as possible.
AM affects horses that are mostly kept at grass and it occurs most often in autumn, although it has also been seen in springtime.
Studies of Seasonal Pasture Myopathy carried out in the United States have linked the condition to seeds from the box elder tree, leading scientists in Europe to examine the role of seeds in AM. In 2013, the seeds of the sycamore tree, commonly known as helicopter seeds (pictured above), were linked to outbreaks of AM in the Netherlands, Germany and Belgium. These seeds are currently considered to be the most likely cause of AM in Europe.
We also know that horses who contracted AM had all been turned out on overgrazed pasture with little fresh grass, dead wood and dead leaves.
However, research on the disease’s triggers is still on-going and many questions — including why AM is becoming more common and, crucially, what could be an effective treatment for it — still need to be answered.
AM can strike fast: owners have reported finding horses quickly transformed from completely healthy to lying in the field, unable to get up.
An affected animal will often be loath to move. The most obvious signs include unwillingness to walk, muscular stiffness or tremors, sweating, dark urine and a high heart rate. The horse could also seem sedated and have difficulty breathing.
Once the clinical signs have shown themselves, the situation is already very serious: the mortality rate at this point is between 70% and 90%.
You must summon a vet the minute you suspect AM because every hour will be crucial. As there is no specific cure yet, vets will do everything they can to make the affected horse more comfortable and relieve his symptoms in the hope this will aid his improvement. The sooner vets reach the animal, the more likely his recovery.
1. Make sure the quality of your horse’s grazing is as high as it can be; if possible rotate his grazing.
2. Manage your paddocks effectively, quickly tackling weeds, dead wood and old leaves.
3. Keep grazing horses away from sycamore trees; if you have sycamore trees in your fields, you could fence them off, although this won’t stop all seeds from reaching the grass.
4. Even if there aren’t any sycamores on your pasture, seeds are able to travel long distances in the air so you need to regularly check for — and remove — them wherever your horse is turned out.
5. Give plenty of additional forage in the form of hay or haylage if the grazing is poor.
6. Avoid having too many horses grazing the same pasture throughout the autumn.
7. Consider bringing your horses in overnight.