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Atypical Myopathy (Sycamore Poisoning)


Atypical myopathy, more commonly known as sycamore poisoning or seasonal pasture myopathy (SPM), is an often-fatal condition which affects your horses’ vital organs including the respiratory system and heart. We have created this post to provide you with information on the causes, symptoms, diagnosis and treatment of sycamore poisoning.


What causes atypical myopathy?

Many of you would have noticed that during autumn and early winter sycamore trees start to drop helicopter seeds, which contain the toxin Hypoglycin A (HGA). Due to the high concentration levels of HGA found in these seeds, when ingested, they can cause atypical myopathy, making your horse feel very poorly. Even small amounts of these seeds can be fatal to your horse, however, each horse is different and their reactions to HGA can vary.


Signs and symptoms of sycamore poisoning

  • Sweating

  • Weakness/lethargy

  • Reluctance to walk or move around

  • Muscle weakness, stiffness or tremors

  • Depression or change in behaviour

  • Signs of colic (but still eating)

  • Increased or laboured breathing rate

  • A high heart rate

  • Choke

  • Dark urine (red or brown colour)

  • Collapse

  • Sudden death

Your horse may appear weak, have difficulty standing or have breathing difficulties, but may still want to eat.

If you spot any of these symptoms or are concerned your horse has been poisoned:

  1. Keep calm and call us as quickly as you can on 01622 737884.

  2. remove your horse (and any other horses) from the field immediately to avoid any further ingestion and ideally, place your horse in a comfortable, bedded stable.

  3. The team at KEH will guide you through what to do and will arrange a vet to attend to you as soon as possible.


Diagnosis for atypical myopathy

If it is suspected that your horse has atypical myopathy, a clinical examination including the taking of bloods and urine will help us make a diagnosis. The most obvious sign that your horse may have atypical myopathy is the presence of red or brown urine, as there are very few diseases that will cause this symptom, this, and taking into consideration where your horse has been grazing, would give us a good indication of the problem and will allow us to quickly start treatment.


Treatment for atypical myopathy

An early diagnosis will enable us to treat your horse as quickly as possible, which is extremely important with this disease. We treat atypical myopathy by administering large amounts of IV fluids which helps to protect your horses kidneys from damage and prevents dehydration. Fluid therapy will need to be carried out within a hospital setting, with regular monitoring from the clinical team. Pain relief would be used alongside the fluids to keep your horse as comfortable as possible.


Although there are a substantial amount of fatalities that result from atypical myopathy, a swift course of treatment in a hospital setting with an experienced clinical team dramatically increases your horses change of recovery, with no long term effects.


Prevent atypical myopathy in horses

Atypical myopathy is a severe and unpleasant disease, and we know that as responsible horse owners you will want to do everything you can to avoid sycamore poisoning. Here are our recommended steps to take:

  • Remove sycamore and any other poisonous trees if you can from your fields, these can then replaced with native, non-poisonous trees to provide shelter for your horse and minimise the impact on the environment.

  • Move your horses away from any paddocks with sycamore trees nearby when helicopter seeds are dropping, or seedlings are sprouting. If this isn’t possible, cordon off any areas around poisonous trees that are within your boundaries and collect and dispose of seeds and leaves safely away from horses.

  • Test for Hypoglycin A in seeds, leaves and seedlings in your field can be carried our through the Royal Veterinary College Diagnostic Service (there is a fee) - https://www.rvc.ac.uk/research/facilities-and-resources/comparative-neuromuscular-diseases-laboratory/diagnostic-services#panel-horse-owners-plant-sample-for-atypical-myopathy-test-and-information

  • Regularly check for any sycamore seeds and saplings and remove them or rake them up as much as possible.

  • Check your neighbouring areas so you're aware of any sycamores nearby – as the wind can blow seeds and leaves into your paddocks.

  • In grazing fields where grass is limited, feed forage such as hay off of the floor in hay nets or feed racks will help avoid fallen seeds in autumn and early winter when seeds fall.

  • Avoid turning out your horse in overgrazed fields as this will increase the risk of your horse eating sycamore seedlings

  • Limit your horse's turnout. Ideally stable horses overnight.

  • Be vigilant of the potential signs of this disease and act quickly if your horse becomes unwell, call the team if you are worried about anything, no matter how small it may seem.

  • Ensure you check your horse regularly at least twice daily.

  • Check your vet insurance is up to date

  • Have an emergency plan in place should you need to contact the vet or transport your horse to the hospital


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