Call to be vigilant about atypical myopathy - Veterinary Practice
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Call to be vigilant about atypical myopathy

THE British Equine Veterinary Association has urged veterinary surgeons to be aware of the clinical signs of equine atypical myopathy (seasonal pasture myopathy) following a surge in clinical cases across the United Kingdom.

Early recognition and treatment are crucial to give the affected horse any chance of surviving this highly fatal muscle disease.

BEVA has provided free online access to two articles on the disease to help vets address the threat.

The disease is found in the UK and Northern Europe and often presents as an outbreak, with affected horses having clinical signs that may include muscle weakness or stiffness, colic-like symptoms, laboured breathing, dark red-brown urine, recumbency or even sudden death.

Toxin in sycamore seeds

Recent research published in the Equine Veterinary Journal shows the disease to be caused by the toxin hypoglycin A, which can be found in the seeds of sycamore trees.

Other trees of the Acer family may also be implicated, with the box elder tree being responsible for outbreaks of SPM, a very similar disorder that is prevalent in mid-western USA and eastern Canada.

Incidences tend to occur repeatedly in the autumn and in the spring following large autumnal outbreaks.

Horses that develop AM are usually kept in sparse pastures with an accumulation of dead leaves, dead wood and trees in or around the pasture and are often not fed any supplementary hay or feed.

Pastures contaminated with sycamore seeds

The high winds this autumn have resulted in considerable contamination of pastures with sycamore seeds. While the seeds may not be directly palatable, horses grazing on poor quality pasture may ingest considerable numbers of them.

The recent surge in cases may become worse through the winter months as access to grass is further limited, says the BEVA.

Early recognition and treatment is essential and since the toxin directly targets aerobic energy metabolism, therapy should be targeted at promoting glucose metabolism and provided fluid dieresis.

Preventive advice for horse owners includes:

  • Supplementary feeding in the field to minimise the risk of horses being tempted to ingest seeds;
  • avoid leaving wet hay on the ground where it will rot;
  • fencing off affected areas;
  • remove seeds where possible;
  • limiting grass turnout; and
  • being 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, and editor of Equine Veterinary Journal, said: “We have seen unprecedented cases of AM since the recent high winds – more than five times as many as this time last year. This dramatic rise appears to be reflected across the UK. It is imperative to spot the symptoms of AM and commence treatment promptly, preferably with hospitalisation of the affected animal to give it any chance of survival.”

Two articles online

The free online articles are:

  • Van Galen, D. and Votion, D.-M. (2013) Management of cases suffering from atypical myopathy: interpretations of descriptive, epidemiological and pathophysiological findings. Part 1: First aid, cardiovascular, nutritional and digestive care. EVJ 25 (5): 264-270.
  • Van Galen, D. and Votion, D.-M. (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. EVJ 25 (6): 308-314.

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