Sycamore Poisoning in Horses

As Autumn approaches leaves start to fall to the ground and it may look like a beautiful and captivating sight. However underneath the beauty there also lurks a dangerous risk to horses, the sycamore seeds.

These seeds are very noticeable (and you probably remember them well from childhood), they are the helicopter seeds that use wind to fly, so that they can be dispersed far away from the parent tree. They are however extremely toxic to horses and with strong winds they can travel very far so even if you have no sycamore trees in your own fields, the seeds can cover a good distance and still pose a risk.


Seasonal Pasture Myopothy (SPM)

Sycamore seeds contain a toxin called hypoglycin A which is found in a number of tree fruits including the sycamore. It causes seasonal pasture myopathy which is a fatal muscle disease and causes a lot of pain and discomfort to horses.

The disease affects the respiratory muscles and so horses are often found lying down and unable to get up without noticeable respiratory effort. According to the Liphook Equine Hospital other symptoms that your horse might be poisoned include;

  • muscle soreness
  • stiffness
  • muscle tremors
  • weakness
  • lethargy
  • fast or laboured breathing
  • reluctance to work
  • red or brown urine

The Liphook hospital emphasises that the results are not always certain death, currently the fatality rate is at 50%, so long as treatment is started early enough. One of the most important issues is rehydration and most horses will need to be professionally seen to either at a hospital or by a vet to give the fluids and also the painkillers needed, as the disease can be extremely discomforting for the horse.


Sycamore Seed Poisoning in the UK and Ireland

An Article in the Derry Journal has highlighted the very real risk that sycamore poisoning poses to horses in the UK and Ireland. Vets are warning all horse owners to be on the look out and to follow these simple guidelines to help reduce the risk of exposure.

  • ensure that horses have adequate feed supplements and forage so that they are not tempted to eat the seeds.
  • remove unused hay that is lying on the ground so that it doesn’t trap fallen seeds.
  • do not prune or cut sycamore trees when they are full of seed, as this can cause a large contamination of the land
  • fields can acquire the seeds through flooding or wind dispersion
  • use fencing if necessary to restrict access to danger areas or remove horses from contaminated pastures.

Horses most at risk according to the BHS are those that are grazed on poor pastures where there is a large quantity of dead wood and leaves. If horses on these sites are not given sufficient extra feed supplements and hay then there is an increased risk of eating seeds and leaves, causing digestion problems as well as poisoning.


poison and toxic leaves for horses
Autumn is a difficult time to manage pasture land for horses (image found on horse

Other Poisonous Leaves – Oak and Acorns

As well as sycamore other plant and tree leaves that can cause damage to horses are oak leaves and acorns. These have to be ingested in quite large numbers and it is relatively rare for horses to ingest large numbers of the bitter seed, according to the Bell-Equine Veterinary Clinic

image oak acorn toxic horses
The acorn fruits of the Oak tree (image found on Pinterest)

Getting rid of acorns can be a tedious and impractical task if your field is located near a large tree, one suggestion is to think of keeping pigs as they will eat them all up with no side effects!

As with most horse health issues it is important to maintain a healthy grazing area and keep it clear of anything that can cause harm. As the weather gets worse and fields become (even) wetter don’t forget about other problems related to field management such as mud fever.

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The sycamore seed (Image found on

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