Autumn is the time of year when owners should be wary of the potentially deadly disease called atypical myopathy. Vet Sarah Hunter explains how horses contract the disease, treatment options and prevention tips.

What is it?

Atypical myopathy is a potentially fatal disease caused by a toxin found in the seeds and seedlings of the common European sycamore, from the Sycamore tree.

This toxin can make its way to the horse’s muscles, causing the muscle cells to become inactive and even die (the disease is fatal in around 70% of affected horses).

The condition is non-contagious and is usually seen in autumn when the sycamore seeds are on the ground, and in spring when the seedlings are growing.

Horses that eat the seedlings or seeds can quickly become affected by the toxin.

What are the signs?

Signs include:

  • lethargy
  • depression
  • a reluctance to move
  • muscle tremors
  • sweating
  • difficulty breathing
  • red/brown urine, due to the products of muscle breakdown being released in the urine.

As soon as you notice these symptoms, call your vet and describe what you’ve seen. Your vet will examine your horse and may take blood and urine samples.

Can I lower the risk?

Ensuring that horses don’t eat sycamore seeds or seedlings is obviously key to preventing the disease. Even if your horse has lived in pasture with sycamore trees before, it is important to be vigilant and take precautions with each tree.

Measures include:

  • fencing off areas around sycamore trees
  • moving your horse to other pastures during risk periods
  • providing extra forage for your horse so that he isn’t tempted to eat any sycamore seeds he finds
  • clearing up sycamore seeds when they have fallen from the tree, and uprooting any seedlings

What’s the prognosis for a sick horse?

To have a chance of recovery, an affected horse will need intensive care at an equine hospital. It can take several days to make a diagnosis from a blood sample and time is of the essence, so treatment may be started before the test results come back.

Unfortunately, there is no antidote, so treatment consists of supportive care, such as fluid therapy, which helps to protect the kidneys from damage, and pain relief.

The first 24-48 hours are the most critical. If the horse survives the first few days, it can still take several months of treatment to make a full recovery.

However, if he does recover, he can often go on to live a normal life and return to full time work without any long-term side effects.

The key is identifying sycamore trees in and around your horse’s field, and doing all you can to prevent him accidentally eating seeds in autumn and spring.

Atypical myopathy is better prevented rather than cured.

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