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Scientists have identified the toxin believed to cause the serious equine disease Atypical Myopathy.

Atypical myopathy, which is often fatal, results in the destruction of skeletal muscle and often the muscle of the heart and diaphragm.  Clinical signs include weakness, muscle tremors, and dark urine with horses frequently laying down and reluctant to stand.  The disease progresses rapidly with many cases developing difficulties eating, breathing and heart problems. The disease may easily be mistaken for colic.

Outbreaks of Atypical myopathy are seen sporadically in the autumn, and occasionally in the spring, often following periods of wet and windy weather. For many years the disease has been linked to pasture, with cases occurring in horses kept on sparse paddocks, although the precise cause was unknown. Earlier this year researchers at the University of Minnesota identified a link between the disease and the Box Elder tree (Acer negundo), which is found in the United States. More recently it has been demonstrated that the same toxin found in the Box Elder tree (known as Hypoglycin A) is also found in the European Sycamore tree (Acer pseudoplatanus), and this is thought to be the cause of the majority of cases seen in the UK.

To reduce the risk of disease it is recommended to avoid grazing horses on fields containing Sycamore trees where possible. If this is unavoidable then plenty of supplemental hay should be provided along with measures to avoid overgrazing the pasture. Reducing turn-out during the at-risk months (October to December) or during regional outbreaks should also be considered. Whilst not all horses appear to be equally susceptible to the disease, young horses and those that have moved paddocks recently appear to be at increased risk.

More information on the current outbreak status in the UK can be found at the following website: