Happiness is in the field: preventing atypical myopathy in grazing horses with rational management of pastures and horses drawn on the basis of the identification of risk factors for disease

Atypical myopathy is a specific disease of horses kept at pastures most of the day. The condition is distinguished by the acute and unpredictable nature of its appearance, its high fatality rate and its rapid evolution. Indeed, over 75% of affected horses die within 72 hours after presenting clinical signs resulting from the severe degeneration of different muscle groups involved in breathing, posture, or the heart muscle.
<br />
<br />There are fewer than ten years, this disease was unknown from the veterinary and equestrian field. More than a dozen European countries are now concerned by this specific disease of equines. Recently, atypical myopathy has also been recognised in the USA.
<br />
<br />Atypical myopathy does not show characteristics of a contagious disease but its occurrence is linked to specific environmental conditions and thus, it emerges in the form of an epizooty: several grazing horses are hit by the disease at the same time and in different regions or even in different European countries. The clinical outbreaks are reported mainly in autumn and spring.
<br />
<br />Occurrence of the clinical syndrome in a horse implies that appropriate circumstances to the onset of the atypical myopathy were present in the host and/or in its environment. Large European epidemiological investigations have identified those circumstances, thus defining risk factors.
<br />These factors are related to the host (e.g. host susceptibility due to age), timing (e.g. season), location (e.g. local geological and ecological factors) and other miscellaneous features (e.g. type of feed, climatic conditions, the use of the horse).
<br />
<br />This review describes management practices at the horse and pasture level in order to reduce the incidence of atypical myopathy in grazing horses.