Sycamore seeds can be dangerous to donkeys

Are sycamore seeds harmful to donkeys and horses?

In a nutshell, yes! It’s relatively recently that the condition known as Atypical Myopathy (sycamore poisoning) has been recognised which is a very serious disease that is caused by donkeys or horses eating sycamore seeds or seedlings. Symptoms of sycamore poisoning in donkeys can come on suddenly and presents as affecting their muscles or causing dullness & lethargy, and their urine turns a very dark red or brown. Sadly, in many cases, equines can die fairly quickly from this poisoning and it is not uncommon for previously healthy animals to be found dead the following day.

Whilst this is thankfully relatively rare and different equines appear to have different tolerances to the toxin due to genetic variations and different grazing habits, it is well worth being vigilant for the seeds in the autumn and seedlings in the spring, especially when your horses or donkeys are in bare paddocks with little else to eat.

The toxin responsible is Hypoglycin A (HGA). The summer of 2022 in the UK saw a prolonged period of drought which caused a bountiful mast year where trees and plants doubled their fruiting & seeds to ensure there are extra left for saplings after all the wildlife have eaten their fill. And as if that wasn’t enough, the drought also caused the sycamore seeds to contain double the toxicity! 

However, to make things even more complicated, not all sycamores are the same. The common Sycamore is Acer pseudoplatanus, but Field Maples look similar & have slightly smaller pink edged seeds which are not toxic. There are even differences between trees and the toxicity of the seedlings can change not only by individual tree but also year on year. You can have your tree tested by the Royal Veterinary College who are conducting ongoing research on Atypical Myopathy, but it is always wise to take preventative measures to minimise the risk of our precious animals eating these deadly seeds.

This autumn, exceptional strong easterly gales have caused a large amount of sycamores to blow quite a distance and have invaded a patch of the dinky donkey paddock. We’ve managed to take as many steps as possible to keep the little guys safe.

How many sycamore seeds would kill a horse or a donkey?

As few as 50 seeds can kill a horse, so little mini horses and donkeys are really vulnerable. The same problem applies to oak trees, with acorns also being toxic to equines, but is more widely known. The same general preventative measures apply to both.

  • Fence of areas around Sycamore trees in autumn so seed fall is contained.
  • Use a leaf vacuum if you can when the helicopter wings are collected in bulk, ideally to be burnt,
  • If you don’t have a leaf vacuum, rake up the seeds regularly and dispose of them.
  • Hand pick remaining seeds using a grid system walking in different directions as they are very easy to miss.
  • Check water buckets & troughs for seeds regularly as the toxins can leach from seeds into the water.
  • Make sure your horses or donkeys have extra food if they are in a bare patch as it will be less likely that they will try to eat any stray seeds.
  • In spring, check for seedlings and pull them up as they appear.
  • Be alert in autumn and spring for any signs of sycamore poisoning. With any unusual signs looking like colic, muscle tremors, apathy or head hanging down, call the vet immediately and remove all horses from the affected area. 

On the positive, the seeds drop over a relatively short period so although you will never eliminate them completely, you can keep your animals safe following these simple precautions. 

A sycamore seed with its characteristic brown colouring.

field maple seed

A pair of Field Maple seeds that are not toxic. Note their lighter colouring, and they can also have pink edges to the wings. The overall shape is shorter and more stubby than the standard Sycamore.

collect sycamore seeds to avoid sycamore poisoning in donkeys and horses
use electric fencing to keep your donkeys safe from sycamore seeds that are toxic to equines

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