Atypical Myopathy

As autumn approaches and the leaves start to be blown from the trees, horse owners need to be aware of a condition called ‘Atypical Myopathy’ (AM), a disease of the muscle. It is caused by a toxin (Hypoglycin A) in the ‘helicopter’ seeds of the sycamore and related types of tree. In autumn, following strong winds, large numbers of seeds falling from trees in a short period pose a risk to horses grazing on surrounding fields.

Signs of AM include sudden onset muscle weakness or stiffness, colic-like signs, heavy breathing, sweating, dark urine and sudden death.

The British Equine Veterinary Association recommend the following to prevent AM:

• Consider fencing off areas around sycamore trees where seeds have fallen
• Remove seeds
• Supply extra hay especially if the pasture quality is poor; horses will not choose to eat the seeds if there is alternative forage available
• Reduce the number of horses on the pasture to allow enough good grazing for each horse
• Stable horses and turn out for short periods of time