Atypical Myopathy In Horses

If your horses live outside all year round, you should be aware of a condition called 'atypical myopathy'. Atypical myopathy can be fatal if not treated quickly. So what causes the condition and how can you protect your horse?

Atypical Myopathy

Atypical myopathy (seasonal pasture myopathy) usually occurs during the autumn and spring months, affecting horses at grass. Although the disease can affect any horse, it is thought that younger animals are more vulnerable.

Atypical myopathy is caused by a toxin contained in the seeds of the sycamore or box elder tree. Grazing horses eat the fallen seeds and ingest the toxin. The poison stops the body's muscle cells from generating energy, effectively killing them.

The poison is extremely potent and death can occur if veterinary attention is not sought immediately.

Symptoms of Atypical Myopathy

Horses affected by atypical myopathy present with a number of symptoms, including:

  • sudden stiffness
  • muscle tremors and shivering
  • colic
  • dark urine
  • high heart rate
  • breathing difficulties

Affected horses may also look depressed and appear lethargic. Suspected cases of atypical myopathy should be treated as veterinary emergencies.

Prevention and Treatment

If you have box elder or sycamore trees growing near your pastures, you should fence them off. Check fields for fallen or wind-borne seeds and remove them.

Horses grazing on poor pasture are especially at risk of atypical myopathy, as they are more likely to eat fallen seeds whilst foraging for grass. Make sure that your horses have plenty of substitute forage to eat if your grazing is poor and limit grazing hours if possible.

Your vet will take blood and urine tests to confirm the diagnosis and your horse will be hospitalised so that intravenous fluids and intensive care can commence. If the condition has been caught quickly and the horse has not eaten too high a volume of seeds, he may make a full recovery.

During the time that your horse is hospitalised, he will be carefully monitored and given pain relief. As the horse recovers, he will be hand fed with a low fat diet and given suitable supplementation.

When your horse is well enough to come home, your vet will give you instructions on a suitable diet and supplement regime to help him recover.

In Conclusion

If your horse grazes on fields near to box elder or sycamore trees, he may be vulnerable to atypical myopathy. If the horse shows any of the symptoms outlined above, seek veterinary attention immediately.