Poisonous Plants - Sycamore

Sycamore trees (also known as Acer pseudoplatanus) are widespread across the UK and a common sight to see in our countryside. However, these trees pose a great threat to the health and welfare of our horses and ponies and their seeds, seedlings and leaves are highly poisonous.

Why is this important for horse owners to be aware of?

The seeds from sycamore trees produce the toxin Hypoglycin A, which is a naturally occurring amino acid in some plants. Metabolism within the horse of Hypoglycin A produces a metabolite which inhibits the use of Acyl Coenzyme-A (CoA) – a crucial factor in numerous biochemical reactions in the body, and disturbs energy metabolism. The resulting disease is known as atypical myopathy. Atypical myopathy is a severe and potentially fatal disease which causes the degeneration and necrosis of postural, skeletal and cardiac muscle (Kruse, 2024). Early identification of trees and seeds and symptoms in horses can be lifesaving.

Symptoms and signs to be aware of:

The most frequently observed symptoms in horses with Atypical Myopathy are weakness, stiffness and reluctance to move, recumbency, trembling, dark-brown urine, abnormally rapid breathing, difficulty exhaling and muscular degeneration. Secondary complications are common such as pressure sores, buccal ulcers, gastric ulcers, choke, diarrhoea, renal dys-function and corneal ulceration. Signs of sycamore poisoning may appear similar to symptoms shown in horses with colic, but still expressing the desire to eat, or tying- up, without being associated to exercise.

What to do if symptoms are observed?

It is advised that if any of these symptoms are spotted or you are concerned you horse has been poisoned you should call your vet as soon as possible and follow any veterinary advice carefully. It is also recommended to remove your horse from the field immediately and move them into a stable or shelter with thick bedding. It is also important to keep the horse warm whilst taking care to not cause them to overheat. All other horses should also be removed from the field. Vets will diagnose atypical myopathy based off results from urine analysis and enzyme levels in the blood.

Preventing Sycamore Poisoning and Atypical Myopathy

1. Sycamore trees within your horse’s fields should be removed to be as safe as possible, however if this is not possible you should fence off areas around the trees allowing enough distance for it to be out of reach from horses. Seeds, saplings and fallen leaves should be raked up, removed and disposed of safely.
2. Horse owners and landowners should be aware of nearby sycamore trees and frequently check fields for any seeds that may have landed where horses are grazing, especially in the Autumn months.
3. Affected horses typically have been turned out in pastures with sparse forage and have often not been given supplemental hay or feed, so providing enough forage for horses should reduce the risk of sycamore seeds being ingested. It is recommended that horses should be fed a minimum of 1.5% their bodyweight in forage per day.
4. Check your horse regularly and familiarise yourself with signs to be aware of in the event that they do become poisoned.