As the season changes vets are urging horse owners to be on alert for signs of the often-fatal condition seasonal pasture myopathy (SPM), formerly known as atypical myopathy.

A horse in the East Midlands has already died in recent weeks of the condition, which is related to the sycamore tree (pictured, top).

The illness weakens the muscles and can present with sudden stiffness, muscle tremors, collapse and colic-like signs.

The fatality rate is around 70% and it is most frequently seen in autumn and spring.

Victims are usually kept in sparse pastures, where seeds on the ground are eaten when there is little grazing.

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Mark Bowen, president of the British Equine Veterinary Association, said: “In the past two years our understanding of this awful condition in horses has increased considerably. We now know that sycamore seeds contain the highly toxic agents that cause SPM and there are practical things that we can advise owners to do that minimise the risk to their animals.”

High winds in 2014 spread the seeds, and the National Equine Health survey recorded four times as many cases as the year before.

H&H vet Karen Coumbe added: “Now is the time of year that problems with this condition are likely to occur. It is too early to know how serious it will be [this year], but hopefully with publicity, owners will be more aware of the condition and how to avoid it.”

Seeds should be cleared from pasture, areas with seeds on the ground should be fenced off and additional forage should be supplied to reduce the chance of horses eating seeds.

Signs of seasonal pasture myopathy

  • Weaknes
  • Muscle trembling
  • Lethargy
  • Pain
  • Dark urine
  • Sweating/shivering