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Atypical Myopathy Update

What is Atypical Myopathy (AM)?

This muscle disease is caused by ingestion of a toxin (poison) which is contained in the seeds, seedlings and leaves of the Sycamore tree - Acer Pseudoplatanus. It is not a new disease, but has become more frequently reported in recent years. It can affect a single horse or alternatively, outbreaks of the disease affecting a number of horses on the same premises can occur.

What signs are seen and why?

The first problem in this disease is the development of severe muscle damage. This occurs because the toxin interferes with the ability of the muscle to undergo its normal processes. Muscle damage can lead to a horse becoming weak and reluctant to move or unable to stand. The disease is painful for the horse and he / she will often show signs of sweatingdistress or reduced appetite. Sometimes swelling or hardening of the muscles is visible and the horse resents being touched. If serious muscle damage occurs, toxic products released from the muscles can become visible in the urine, this can lead to 'red-wine' or 'coffee' coloured urine. These muscle break-down products can unfortunately damage the kidneys and secondary kidney failure can arise. Horses affected by Atypical Myopathy (AM) can also have difficulty urinating and become unable to empty their bladders normally. Sometimes the respiratory or heart muscles become affected, leading to difficulties breathing or the development of heart failure. Sadly this disease is often fatal, with variable survival rates reported from different areas, ranging from 3-57%.

What can I do to minimise the risk of my horse developing AM?

  • Regularly inspect the pasture for sycamore seeds, leaves or seedlings and remove them if seen.
  • Check surrounding areas for the presence of sycamore trees. The 'helicopter' seeds can be carried a long way in the wind.
  • Fence off any contaminated areas of pasture.
  • Remove horses from the pasture while this is done.
  • Provide extra forage (hay or haylage) as some seeds will remain on the pasture and in spring the seeds germinate rapidly and new seedlings will appear daily. This extra forage reduces the likelihood of the seeds or seedlings being eaten.
  • Reduce the stocking density on a pasture so that there is plenty of grass for the horses to eat.

Unfortunately the above measures do not completely eliminate the risk and full time stabling is the safest way to manage at risk horses in the autumn and spring. Full time stabling brings its own risks in horses that are usually turned out. The best compromise for each horse will depend on: the frequency with which the pasture can be checked and cleared of sycamore seeds / seedlings and the horse's ability to tolerate full time stabling.

What should I do if I think my horse has AM?

If your horse shows any of the signs described above, we recommend contacting your vet immediately.

Will it be clear to my vet whether my horse has AM?

If a horse has advanced signs of AM then signs will likely be strongly indicative of the disease. However, if the disease is detected in the early stages, it can be difficult to say for certain whether or not it is AM. A number of other conditions including various forms of colic, equine grass sickness, other muscle diseases and a number of neurological conditions can lead to similar signs. There is not a definitive diagnostic test for the disease and this can make early diagnosis challenging. However, a simple blood sample will allow us to see whether the horse has muscle damage.

Early detection of any of the above described signs and prompt discussion with your vet should lead to the highest likelihood of a positive outcome for you and your horse.

For further information or if you have any queries, please feel free to contact us at BELL on 01622 813700. There is also further information on Atypical Myopathy in our 'useful info' section under 'poisonous plants'.