Not all maple species dangerous to horses

Press release Utrecht University/RIKILT Wageningen UR

The Faculty of Veterinary Medicine at Utrecht University and RIKILT Wageningen UR have studied equine mortality as a result of atypical myopathy. This serious muscular disease can occur after eating the leaves, seeds and/or buds of maple trees that contain the toxic substance hypoglycin A. The scientists studied hundreds of samples taken from a wide range of maple species to find out which species contained the toxin. They found that the sycamore maple contained the toxin, but the field maple (or hedge maple) and the Norway maple do not.

Each year, hundreds of horses in Europe die due to atypical myopathy, also known as ‘pasture myopathy’. In the past, horses with the condition were almost certain to die, but today the disease can be diagnosed and treated at a much earlier stage. However, the mortality rate for the disease is still 70%, so prevention is extremely important.

Appeal to horse owners
Atypical myopathy is caused by the substance hypoglycin A, which is present in some species of maple, but not in others. For owners of horses with maple trees around their pastures and paddocks, it is therefore vital to know which species of maple they are dealing with. The researchers called on horse owners to send samples of the maple trees in their vicinity. They received 278 samples of the three most common types of maple trees in the Netherlands: the sycamore maple (Acer pseudoplatanus), the field maple or hedge maple (Acer campestre) and the Norway maple (Acer platanoides). They then measured the concentration of hypoglycin A in all of the seeds, leaves and buds. No levels of the toxin were found in field maples or Norway maples, but every sample of the sycamore maple contained hypoglycin A. It seems therefore that field maples and Norway maples near pastures and paddocks do not pose a danger to horses.

Sycamore maple not necessarily unsafe
The presence of hypoglycin A in the leaves, seeds and buds of the sycamore maple does not necessarily mean that the tree is by definition unsafe. There are thousands of pastures with sycamore maples in Europe in which the horses do not become ill. The level of the concentration of hypoglycin A also does not appear to correlate to whether or not horses nearby will become ill, so it seems as if there are other factors that play a role in the development of the disease.

Preventive measures
The researchers recommend that horses with full access to a pasture surrounded by sycamore maple trees are given plentiful amounts of good quality roughage in their feed during autumn (placed on a dry spot on the ground), and are provided with places to take shelter. Owners may also fence off the edges of the pasture with electric fences to increase the distance to the trees and block access to the leaves and seeds. If necessary, they can also use a leaf blower to remove leaves and seeds from the pasture. The researchers also recommend keeping the horses inside during storms until the branches, leaves and seeds blown from the trees can be removed. In order to ensure the horses’ welfare, it is of course better to invest time and effort into keeping pastures leaf-free than to keep the horses in their stalls for long periods of time.

The study of maple trees was published in Journal of Veterinary Internal Medicine

More information
Marieke Veldman, Communications Department, Faculty of Veterinary Medicine, Utrecht University, (030) 253 3430,
Or: Utrecht University Press Relations, (030) 253 3550, or Jeannette Leenders,  RIKILT Wageningen UR, 0317 480245,