Protect your horse from atypical myopathy

With autumn in full swing and sycamore seeds falling fast, the British Equine Veterinary Association reminds owners to take steps to minimise the risks of their horse contracting atypical myopathy

It’s that time of year again, and sparse fields and gusty autumn weather create the perfect conditions for horses to contract atypical myopathy. Caused by the ingestion of sycamore seeds, the disease is fatal to equines. Although horses don’t typically choose to eat sycamore seeds, when pastures are bare, there’s a higher tendency for them to be ingested by accident as they forage for every blade of grass. Wind can also spread the seeds faster and further, potentially reaching fields where there are no sycamore trees present.

A member of the maple tree family, sycamore trees are a source of the toxin hypoglycin A. It disperses its helicopter shaped fruit that distributes seeds over long distances, typically several hundred metres, but reportedly up to 4km. The toxic dose of sycamore seeds can vary from less than 100 to several thousand single seeds. With each tree potentially shedding more than 20,000 double seeded ‘helicopters’, the amount found on horses’ fields can be considerable. In the spring, seedlings represent a risk to horses and can affect hay made from contaminated pasture. Seedlings at the edge of watercourses can also contaminate water supplies, especially when trampled as horses walk across them.

Symptoms

The most consistent clinical sign of atypical myopathy is the passing of dark brown urine (myoglobinuria) as a result of muscle breakdown. Horses usually become weak and reluctant to move and may lie down, but usually have a normal or increased appetite. In the most severe cases a horse will develop very severe colic-like signs due to significant pain. In some horses the severity of muscle pain leads to euthanasia on welfare grounds. These signs occur as a result of the active toxin that prevents muscles from undergoing normal energy metabolism. It can affect all muscles in the body, including the respiratory muscles and heart.

“It’s imperative to contact your vet as a matter of urgency if you’re concerned your horse may be suffering from atypical myopathy,” said BEVA President, Huw Griffiths. “We can use a special blood test, thanks to research funding from The Horse Trust, to diagnose and measure exposure to the toxin. The earlier we’re able to intervene the more likely a favourable outcome for the horse.”

Actions you can take to limit your horse’s access to sycamore seeds are…

• Identifying trees both around and near your horse’s field. Trees are often easiest to identify in the summer when in full bloom, rather than in the autumn, when leaves have largely fallen. The characteristic maple leaf shape is easy to spot although, if in doubt, a test’s available from the Royal Veterinary College as a result of work funded by The Horse Trust
• Collecting seeds or excluding horses from affected areas using electric fencing
• Feeding supplementary hay to try and prevent horses from excessive foraging for short blades of grass and inadvertent ingestion of seeds. However, you’ll need to ensure the hay doesn’t become contaminated by seeds
• Not rashly felling trees when laden with seeds as this can cause a sudden and considerable contamination of the pasture. Consider local regulations, tree protection orders and tree ownership if felling’s the only option
• Monitoring your horse carefully, even after they’ve been moved from the affected pasture, as disease can occur up to four days after exposure