Press release

Not all Acer species are dangerous for horses

Published on
April 13, 2016

The Faculty of Veterinary Medicine at Utrecht University and RIKILT Wageningen UR carried out a joint study to determine the mortality rate of equine atypical myopathy. This severe muscle disorder can occur after eating Acer leaves, seeds or shoots that contain the toxin hypoglycin A. The researchers took hundreds of Acer samples to determine in which species this toxin could be found. The toxin was detected in the sycamore but not in the field maple or the Norway maple.

Hundreds of horses die each year in Western Europe of equine atypical myopathy, also known as atypical myoglobinuria or EAM. While this form of myopathy used to be fatal, these days the condition can be detected and treated at an earlier stage. Despite the available treatment options, however, the condition still has a 70% mortality rate. Prevention is therefore crucial.

Raising awareness among horse owners

Equine atypical myopathy is caused by the substance hypoglycin A, which is present in some Acer species. Horse owners who have Acer trees in their pastures and paddocks should know how to identify the species of tree. The researchers invited horse owners to submit samples of their Acer trees. They received 278 samples of the three most common species of Acer in the Netherlands: the sycamore (Acer pseudoplatanus), the field maple (Acer campestre) and the Norway maple (Acer platanoides). Concentrations of hypoglycin A were measured in all seeds, leaves and shoots. While the toxin was not detected in the field maple or the Norway maple, the researchers did find concentrations of hypoglycin A in all samples of the sycamore. This suggests that the field maple and the Norway maple are perfectly safe in paddocks and pastures.

Sycamore not necessarily dangerous

The presence of hypoglycin A in the leaves, seeds and shoots of the sycamore doesn't necessarily make this species dangerous. Many thousands of pastures in which sycamores grow do not have any incidence of equine atypical myopathy. The researchers did not find a link between concentrations of hypoglycin A and the incidence of sick horses. This would suggest that other factors play a role in the condition.

Prevention measures

The researchers recommend that all horse owners provide their horses adequate shelter and supplement their feed with plenty of high-quality roughage (left in a dry place). This is particularly important for horses with unrestricted access to pastures in which sycamores grow. Horse owners can also create a leaf-free and seed-free grazing area by sectioning off part of the pasture with electric fences to ensure a safe distance from the trees. If necessary, they can also use a leaf blower to remove the leaves and seeds. Horses should be kept inside during stormy weather until all fallen branches, leaves and seeds have been removed. To ensure the health of the animals, it is better to keep pastures leaf-free instead of housing the horses indoors for long periods of time.


The research study on Acer was published in the Journal of Veterinary Internal Medicine.