Each season brings new focuses and challenges when caring for your horse. When summer comes to a close, a particular threat comes from sycamore & ‘helicopter seeds’. Atypical myopathy (AM) can occur at different times of the year. The highest risks are in autumn when maple leaves and seeds fall to the ground, but seedlings in spring can also be a risk.
Before you start planning your winter feeding and health regimen, it is worth considering the risk of Atypical Myopathy. This disease can be fatal in horses, so it is worth considering what causes it, and how it might be prevented.
What Is Equine Atypical Myopathy?
Equine atypical myopathy is an often fatal muscle disease. It’s linked to the ingestion of seeds from maple trees, typically sycamore seeds. It’s also known as seasonal pasture myopathy due to the increase in cases in grazing horses in autumn when the seeds fall from the trees.
The disease affects several systems in the horse’s body, including the respiratory and circulatory systems. It results in muscular weakness and stiffness. It requires early intervention, as 75% of cases are fatal within 72 hours.
Causes of Atypical Myopathy
Atypical myopathy in horses is connected to a toxin known as hypoglycin A. While the highest risk is from seeds in the autumn, it’s also possible to see cases in the spring caused by the ingestion of seedlings. The toxin is present in the seeds, seedlings and leaves of Acer pseudoplatanus trees, such as sycamores.
The concentration of hypoglycin A can vary. But it’s best to err on the side of caution when it comes to grazing near these trees. It can only take a relatively small amount of seeds to cause a problem.
It’s worth noting that water that has come into contact with seedlings can also contain the toxin. This increases exposure and potentially goes over the maximum amount of hypoglycin A that a horse can tolerate.
Atypical Myopathy Symptoms and Diagnosis
Noticeable signs to look out for are:
- Shortness of breath
- Stiffness
- Struggling to walk or stand
- Brown or dark red urine
- Low hanging head
- Trembling
- Colic-like symptoms without a reduction in appetite
While there are a variety of tests that can help a vet diagnose AM, reported symptoms and observation are usually used initially. The clinical signs include:
- Heart problems
- Brown or dark red urine
- Laboured breathing
- Weakness
- Muscle tremors
The vet may also take a blood sample to check parameters such as muscle enzymes and kidney values.
Atypical Myopathy Treatment
It’s essential to act fast, which is why observation is crucial to diagnosis. In many cases, atypical myopathy treatment will start before official confirmation of the disease through testing. Horses require round-the-clock advanced care in specialist equine hospitals, which will involve intravenous fluid therapy and supportive care.
Treatments are selected by the vet and will focus on reducing the risk of ongoing damage from the toxins, rehydration and muscle healing. Treatments may involve:
- Rest
- Rehydration - intravenous fluid therapy
- Insulin and glucose supplementation
- Carnitine
- Vitamin E
- Riboflavin
- Selenium
- Pain relief
- Keeping warm
- Muscle relaxants
If horses survive the first few days, they typically go on to make a full recovery. However, it can take months to return to full health.
[H2] Equine Atypical Myopathy: Focusing on Prevention
Throughout the year, you focus on gut health and providing the best care for your horse. Mitigating the risks of atypical myopathy needs to be part of your routine. Since it can be fatal and early diagnosis and treatment are vital, prevention is where you should focus your attention.
Our first tip is to identify and remove any poisonous trees on your land, especially those near your pasture. As sycamore seeds are light and have wings, they’re easily carried by the wind. So, keep in mind that trees that aren’t on your land can also be the culprit.
We recommend replacing the trees with non-poisonous varieties. Horses gather under the trees for shelter and shade, and our environment needs them. If you can’t remove the sycamore trees, the second best option is to move horses away during autumn when seeds begin to drop and in spring when seedlings sprout, or fence off the majority of the ‘drop zone’ under and around the tree.
Collecting and disposing of seeds and saplings is also an option. It’s not a plan that guarantees success, and it requires effort. However, you can add it to other strategies, such as moving the horses away. It’ll reduce the risk of seeds being blown into other areas. We recommend regular monitoring and a rake (or even paddock vacuum). Chemical management such as spraying could also be an option.
Vigilance is required. For particularly windy days, you might want to limit turnout, and ideally, you’ll stable your horse overnight. Checking for seeds is the first step. However, looking for early signs of the disease is also crucial for early intervention.
Key Takeaways
Atypical myopathy in horses is caused by the ingestion of hypoglycin A, a toxin found in acer seeds, including sycamores. It causes metabolic problems that affect the heart and respiratory system and can be fatal.
Early treatment is key, so look out for signs such as shortness of breath, stiffness, hanging head and trembling. The best approach is prevention, which means keeping your horse away from falling seeds in the autumn and seedlings in the spring.
