Atypical myopathy is a mysterious illness, usually found in grazing horses — mostly in the autumn and spring — which has been linked to the seeds of the sycamore tree.

It has a fatality rate of 70% and once a horse is exhibiting signs the condition is typically already serious. Some horses have made a successful recovery after being treated with intravenous fluids and intensive care.

Signs of atypical myopathy include muscular weakness and stiffness, dark urine, fatigue, colic-like signs, shivering, sweating and trembling. The onset of the illness can be extremely rapid, with some horses being found dead in their fields.

It is recommended that horses are not grazed in fields that contain sycamore trees, or on pasture that borders them in order to reduce the likelihood of coming into contact with the seeds.