The dramatic rise in cases of Atypical Myopathy in the UK last autumn has prompted the British Equine Veterinary Association (BEVA) to remind vets to remain on high alert for further outbreaks this spring. Early diagnosis is essential to give the best chance of survival of this highly fatal disease.

Atypical Myopathy is a serious muscle disease found in the UK and Northern Europe. It is linked to horses eating the seeds from trees in the Acer family, including sycamore and box elder. There were more than five times as many cases of AM last autumn than in the previous year and experts have warned that the disease tends to occur more frequently in the spring following an autumn surge, possibly because of the growth of seedlings. The prognosis is poor, with survival rates of less than 25%.

Horses that develop AM are usually kept on sparse pastures, near trees from Acer pleudoplatanus (sycamore) or Acer negundo (box elder) that shed seeds containing the toxin hypoglycin A. They are often not fed any supplementary hay or feed and may be driven to browse on an accumulation of dead leaves, dead wood and trees in or around the pasture but sometimes well-fed animals are affected. While the tree seeds may not be directly palatable, horses on poor quality grazing may ingest considerable numbers of them.

The clinical signs of AM may include muscle weakness or stiffness, colic-like symptoms, laboured breathing, dark red-brown urine, recumbency or even sudden death. Often the disease will present as an outbreak. Confirmation of diagnosis is by a blood or urine test. The toxin directly targets aerobic energy metabolism so therapy should be targeted at promoting glucose metabolism and provided fluid dieresis.

Preventative advice for horse owners includes:

  • Check spring pasture carefully for seeds prior to turnout
  • Limit turnout if you are concerned about seed presence and ensure horses are well-fed prior to turnout
  • Provide supplementary feeding in the field to reduce the risk of horses being tempted to ingest seeds
  • Avoid leaving wet hay on the ground where it will rot
  • Fence off affected areas
  • Be aware that a field without sycamore trees can still contain seeds spread by high winds or flood water

Professor Celia Marr, Partner at Rossdales, Newmarket, European Specialist in Equine Internal Medicine and Editor of Equine Veterinary Journal said: “New, collaborative research, instigated last year between the University of Liege, the Irish Equine Centre and the Animal Health Trust should shed more light on the characteristics of the disease in this country. Once we know more about the specific causes we should be able to make more positive progress with prevention strategies.”

BEVA has provided free online access to two articles from the journal of Equine Veterinary Education on the disease for all vets to help them address the threat.

Volume 25, Issue 5, pages 264–270, May 2013

Management of cases suffering from atypical myopathy: Interpretations of descriptive, epidemiological and pathophysiological findings. Part 1: First aid, cardiovascular, nutritional and digestive care (pages 264–270) G. van Galen and D -M Votion.

Volume 25, Issue 6, pages 308–314, June 2013

Management of cases suffering from atypical myopathy: Interpretations of descriptive, epidemiological and pathophysiological findings. Part 2: Muscular, urinary, respiratory and hepatic care, and inflammatory/infectious status (pages 308–314) G van Galen and D - M Votion.