Sycamore Poisoning In Horses

Sycamore Poisoning In Horses: What You Need To Know

Sycamore poisoning, or atypical myopathy, is a very real and worrying danger for horse owners. In fact, this severe and potentially fatal muscle disorder is particularly concerning for owners who turn their horses out to pasture. After all, it can be tricky to monitor whether your horse is grazing on the different parts of a sycamore tree that’s nearby.

To help you keep your horse happy and healthy, we’ve compiled a list of signs and symptoms of atypical myopathy to watch out for, as well as what to expect if your horse needs treatment. Early detection and intervention are critical in your horse’s survival, though, which is why it’s essential to educate yourself on the condition. So let’s get right into it.

What is Sycamore Poisoning?

Sycamore poisoning, also known as atypical myopathy, is a severe and potentially fatal muscle disorder that primarily affects horses. This condition is usually caused when horses ingest a toxin called hypoglycin A (HGA). This is found in the trees, leaves, seeds, and seedlings of sycamore trees.

When horses ingest the toxin, it stops energy production in the muscle cells and affects the hearts and the muscles that are responsible for breathing and moving. The disease typically occurs when a horse eats the helicopter seeds or sycamore seedlings, which is why it’s so important to check the horse’s pasture for potentially poisonous plant material.

Atypical myopathy can affect individual horses or multiple horses in the same group, but some horses may be more susceptible to the toxin due to genetics or their grazing habits. Still, horses of any age, sex, and breed can develop atypical myopathy, although young horses may be more susceptible since they spend more time outside.

Prompt diagnosis of any affected horses is crucial for their survival since the atypical myopathy can spread quickly. Additionally, the survival rate is already low and is only around 30% to 40%.

Sycamore poisoning in horses

Are sycamore trees poisonous to horses?

Sycamore trees, specifically the Acer Pseudoplatanus species, can be toxic to horses. However, not all species of sycamore trees have HGA in their seeds or any other parts, so distinguishing between different types of sycamores can be tricky. If you’re in doubt, it’s best to keep your horses away from these trees altogether.

Are sycamore leaves poisonous to horses?

There isn’t much information about whether the leaves of the sycamore tree are particularly poisonous. But, considering that other parts of the tree can cause atypical myopathy, it’s best to stop your horses from eating any fallen sycamore leaves.

If there are any overhanging sycamore trees near their pasture, you may want to consider moving them away from the trees. Alternatively, you can try to clear fallen sycamore leaves from the pasture as often as you can.

Are sycamore seedlings poisonous to horses?

Sycamore seeds and seedlings are the most poisonous parts of the sycamore tree. They have a particularly high concentration of HGA, and while the specific concentration of sycamore seeds varies, it’s best to keep your horses away from them to prevent atypical myopathy.

Signs of Sycamore Poisoning in Horses

The symptoms of atypical myopathy can vary depending on how severe the condition is in your horse. Severely affected horses may exhibit almost all of these signs or symptoms, so it’s important to monitor your horse’s behaviour closely.

If you notice any of the following signs, it’s important to contact your local equine veterinary surgeon immediately. Atypical myopathy is considered an emergency and requires prompt treatment.

The most common symptoms of atypical myopathy include:

  • Muscle weakness: Some horses may struggle to walk, stand, or move properly. You may notice that they have mild to severe muscle weakness, which can make it difficult for them to move.
  • Dull appearance and low head carriage: When a horse has atypical myopathy, they are usually lethargic and will carry their heads much lower than usual.
  • Muscle trembling or tremors: Tremors or involuntary muscle spasms are common in affected horses.
  • Colic-like symptoms: In some cases, a horse may exhibit colic-like behaviour like shivering and sweating. However, they usually keep their appetite and will eat and drink normally.
  • Brown or dark red urine: When your vet takes a urine sample, it may range in colour from dark red to muddy brown.
  • Heart and respiratory problems: Severely affected horses can sometimes develop heart and lung complications, which may make it difficult for them to breathe.
  • Sweating: Excessive sweating is common in horses with atypical myopathy, particularly in young horses.
  • Change in behaviour: As a horse owner, it’s not unusual to be familiar with your horse’s personality and behaviour. So, when it changes, it can be alarming. Horses with atypical myopathy may have a drastic change in behaviour or seem depressed.
  • Increased or laboured breathing: Since the condition can affect the lungs, it’s not uncommon for horses to have difficulty breathing. It may sound laboured or be quick and frantic.
  • Choking: Because your horse may not be able to breathe or swallow properly, it may be more susceptible to choking when it eats or drinks.
  • Sudden death: In more severe cases, horses that have atypical myopathy may experience sudden death. But it’s important to remember that sycamore poisoning doesn’t mean your horse is going to die. In fact, plenty of horses survive with prompt intervention and early detection.

How to Treat Atypical Myopathy

Atypical myopathy can be tricky to diagnose and treat. Still, standard treatment methods include a combination of supportive care, symptom management, and intense medical intervention. Some of the most common approaches include:

Early intervention

Once your local vet has assessed your horse, they will typically take blood samples and run other diagnostic tests to confirm the diagnosis. However, confirmation of atypical myopathy can take several days.

Since the condition is more serious than others, treatment is usually started before receiving confirmation. Early intervention is essential if you want to improve your horse’s chance of survival and long-term recovery.

Supportive care

Horses that develop severe atypical myopathy may need to be hospitalised at a special equine veterinary hospital so that they can receive round-the-clock care. Their care will include intravenous fluid therapy to protect your horse’s kidneys from damage and to prevent dehydration.

Pain relief

Atypical myopathy can be a painful and incredibly uncomfortable condition for your horse. So, when your horse is hospitalised, they are usually administered pain medication like painkillers and anaesthetic drugs.


Unfortunately, there isn’t a specific antitoxin available for the ingestion of sycamore seeds or other parts of the sycamore tree. However, there are several types of medication that can help to prevent the absorption of HGA. This can stop the condition from worsening and can increase the chances of your horse’s survival.

Vitamin supplementation

Supplementary vitamins and minerals may help to support muscle cell function and can sometimes act as antioxidants to rid your horse of any toxins from the sycamore seeds. Generally, horses are given a cocktail that includes vitamins B1 and B2, vitamin C, vitamin E, and carnitine.


Although atypical myopathy has relatively high mortality rates, most horses that can survive the initial recovery period have a good chance of recovering completely. It’s important to remember that the recovery can be quite slow, so be sure to take it easy on your beloved horse while they’re getting back on their feet.


How many sycamore seeds can kill a horse?

The exact number of sycamore seeds that it will take to kill a horse will depend on the concentration of HGA in the seeds. Since some trees have a higher concentration in their leaves and seeds than others, it’s hard to say how many seeds your horse can ingest before passing away. Some horses may also be more sensitive to the toxin than others, which means it will take fewer seeds to kill them.

How much sycamore can kill a horse?

If your horse eats any part of the sycamore tree, it’s likely to fall ill quickly. No matter how many leaves or seeds your horse ingests, the HGA toxin has a severe and almost immediate effect. So, it’s best to keep your horse away from any sycamore trees, leaves, seeds, or seedlings when they are turned out to pasture.

Similar Posts