However good a person’s pasture management, there will always be some residual risk of poisonous plants, shrubs and trees. In recent years there has been a marked increase in cases of sycamore (Acer pseudoplatanus) poisoning.
Sycamore leaves, seeds and seedlings contain toxins hypoglycin A (HGA) and methylene cyclopropyl glycine (MCPG), which cause a severe and often fatal muscle disorder called atypical myopathy.
“Atypical myopathy isn’t an infectious disease, but it is an epidemic form. We are seeing cases everywhere across Europe, and we know that they’re increasing. Strangely, it’s an emerging disease caused by a tree that has been present in Europe for hundreds of years,” says Dominique Votion, who is leading research into the condition. “Sadly, around 75% of horses do die from it, but it’s not always fatal. If horses are hospitalised and can receive intensive care they are more likely to survive.”
Atypical myopathy occurs seasonally, with the risk factor the greatest in the spring (1 March to 31 May), when saplings start to grow, and in the autumn (1 October to 31 December), when the tree produces samaras, the double-winged seed pods known as ‘helicopter’ seeds.
“The amount of seedlings produced does vary year on year. When you have a very dry summer, followed by strong winds in the autumn, large quantities of seeds fall,” says Dominique.
“Sycamore samaras can travel for several hundred metres and so pasture contamination with seeds or seedlings isn’t necessarily linked to the presence of a tree on the pasture. In fact, studies indicate that 80% of horses who contracted atypical myopathy did so when grazing in a pasture that had never before had any cases.”
How to limit the risk of atypical myopathy
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