New research has shown that the seeds of the sycamore tree can cause atypical myopathy.
Sycamore trees could be killing horses, according to a new study published this month in the Equine Veterinary Journal.
Researchers have discovered that toxins from the seeds of the tree, Acer pseudoplatanus, are the likely cause of atypical myopathy (AM) in Europe – the common name for this tree is sycamore in the UK, but it is also known as the sycamore maple in some other countries.
The new research follows a study in the USA earlier this year that has linked toxins from the box elder tree (Acer negundo) with seasonal pasture myopathy (SPM), the US equivalent of AM2.
Atypical myopathy is a highly fatal muscle disease in northern Europe, and over the past 10 years, approximately 20 European countries have reported the disease with incidences tending to occur repeatedly in the autumn and in the spring following large autumnal outbreaks.
Research was conducted by an international team led by Dominic Votion from the University of Liège and involved 17 horses from Belgium, Germany and the Netherlands, suffering from atypical myopathy.
High concentrations of a toxic metabolite of hypoglycin A were identified in the serum of all of the horses. The pastures of 12 of the horses were visited by experienced botanists and the A pseudoplatanus, the sycamore maple, was found to be present in every case. This was the only tree common to all visited pastures.
Scientists believe hypoglycin A is the likely cause of both AM in Europe and SPM in North America. The sycamore and the box elder are known to produce seeds containing hypoglycin A and the pastures of the afflicted horses in Europe and the USA were surrounded by these trees.
Researchers at the universities of Minnesota and Liège are continuing their work to try to uncover exactly how the equine disease occurs.
Discussing the ongoing research, Adrian Hegeman from the University of Minnesota said: “It is likely that the most important contributing factors to horses becoming poisoned by hypoglycin A are the availability of seed in the field combined with lack of other feeding options.
“The seeds from two species of maples (box elder and sycamore maples) that we have tested include significant quantities of hypoglycin A. We know that seeds contain highly variable quantities from seed to seed, even within a single tree.
“We do not know yet how hypoglycin A levels vary seasonally, nor do we know how its abundance varies with different levels of stress to the plant, though this may well explain seasonal variability in the occurrence of the malady.
“It is possible that conditions that stress the plants may contribute to significant seasonal changes in hypoglycin A levels. At this point, we just don’t know. It is common held knowledge that trees under stress usually produce more seed.”