European outbreaks of atypical myopathy in grazing horses (2006-2009): determination of indicators for risk and prognostic factors.
Authors: van Galen G, Saegerman C, Marcillaud Pitel C, Patarin F, Amory H, Baily J D, Cassart D, Gerber V, Hahn C, Harris P, Keen J A, Kirschvink N, Lefere L, McGorum B, Muller J M V, Picavet M T J E, Piercy R J, Roscher K, Serteyn D, Unger L, van der Kolk J H, van Loon G, Verwilghen D, Westermann C M, Votion D M
Journal: Equine veterinary journal
Summary
Between 2006 and 2009, researchers across Europe systematically analysed 354 confirmed or probable atypical myopathy (AM) cases reported to the Atypical Myopathy Alert Group, alongside 69 non-AM cases with similar presentations, to establish diagnostic criteria and prognostic indicators that could refine both clinical management and prevention strategies. Environmental risk factors proved diagnostically valuable: the presence of dead leaves, wood and fallen trees on pasture, combined with sloping terrain, full-time grazing without supplementary feeding, and normal body condition, distinguished AM from other myopathic conditions, whilst pigmenturia, maintained normothermia and congested mucous membranes further supported diagnosis. Among the 354 AM cases (26% survival rate), nonsurvival was strongly associated with recumbency, sweating, anorexia, and signs of respiratory or cardiovascular compromise (dyspnoea, tachypnoea, tachycardia), whereas horses remaining ambulatory with normal temperature and mucous membrane perfusion, continued defaecation, and receiving vitamin and antioxidant supplementation demonstrated improved outcomes. For practitioners managing suspected AM, these findings emphasise the critical importance of early intervention to maintain ambulation, aggressive antioxidant and micronutrient support, and preventive pasture management—particularly removal of fallen wood and leaves, restriction of spring/autumn pasture access, and dietary supplementation during high-risk periods. This multi-centre analysis substantially refines risk stratification and prognosis, enabling evidence-based decision-making in what remains a challenging condition.
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Practical Takeaways
- •Pasture management is critical for AM prevention: clear dead plant material, avoid sloping pastures for grazing, and provide supplemental feed even when pasture is available
- •Early clinical assessment of stance (standing vs. recumbent) and vital signs can help predict outcome; recumbent horses with tachycardia and tachypnoea have poor prognosis
- •Supportive care including vitamin and antioxidant supplementation should be initiated immediately in suspected AM cases to improve survival chances
Key Findings
- •Among 354 confirmed or highly probable AM cases across Europe (2006-2009), survival rate was 26%
- •Risk factors for AM included presence of dead leaves/wood/trees on pastures, sloping pastures, full-time pasture access, and absence of food supplementation
- •Nonsurvival was associated with recumbency, sweating, anorexia, dyspnoea, tachypnoea and/or tachycardia
- •Survival was associated with remaining standing, normothermia, normal mucous membranes, defaecation, and vitamin/antioxidant therapy