Table 3: Risk and protective factors for the development of atypical myopathy.

Risk factors Protective factors Demographic data      Age Young horses (<3 years)    Sex* (i) Colts  (ii) Stallions Geldings  Body condition (i) Thin  (ii) Normal weight (i) Overweight Management practices at the horse level      Deworming   Frequent deworming  Vaccination   Regular vaccination  Occupation   Training  Pasturing Full-time pasturing (all year round) (i) Not at pasture  (ii) <6 H per day at pasture  (iii) Weather-dependant pasturing in spring and in autumn Food and water      Supplementary feeds Hay in autumn (i) Supplementary feeds in autumn (except hay), in particular silage and complete mix  (ii) Supplementary feeds in winter, in particular straw, silage, complete mix, and corn  (iii) Supplementary feeds in spring  (iv) Supplementary feeds in summer  (v) Salt block (all year round)  Water supply   (i) Distribution network  (ii) In tank or bath tub Pasture characteristics      History Dead horses on the pasture in the past    Grass land Lush pasture in winter    Incline (i) Sloping pasture  (ii) Steep slope Gentle slope  Trees (i) Surrounded by or containing trees  (ii) Presence of dead leaves  (iii) Presence of dead wood    Humidity (i) Humid pasture  (ii) Pasture surrounded by or containing a stream/river   Management of the pastures       Spreading of manure

*Age was identified as a confounding variable regarding the risk factors associated with the animal’s sex. Sex is linked to age, as “gelding” is a status that follows castration, a procedure usually performed in males >18 months old (i.e., the most risky age for AM). Because females are more frequently kept at pasture than males, a higher percentage of AM cases is females.