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Seasonal pasture myopathy/atypical myopathy in N orth A merica associated with ingestion of hypoglycin A within seeds of the box elder tree
Author(s) -
Valberg S. J.,
Sponseller B. T.,
Hegeman A. D.,
Earing J.,
Bender J. B.,
Martinson K. L.,
Patterson S. E.,
Sweetman L.
Publication year - 2013
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/j.2042-3306.2012.00684.x
Subject(s) - metabolite , urine , myopathy , ingestion , chemistry , biology , biochemistry , medicine
Summary Reasons for performing study We hypothesised that seasonal pasture myopathy ( SPM ), which closely resembles atypical myopathy (AM), was caused by ingestion of a seed‐bearing plant abundant in autumn pastures. Objectives To identify a common seed‐bearing plant among autumn pastures of horses with SPM , and to determine whether the toxic amino acid hypoglycin A was present in the seeds and whether hypoglycin metabolites were present in SPM horse serum or urine. Methods Twelve SPM cases, 11 SPM pastures and 23 control farms were visited to identify a plant common to all SPM farms in autumn. A common seed was analysed for amino acid composition (n = 7/7) by GC‐MS and its toxic metabolite (n = 4/4) identified in conjugated form in serum [tandem mass spectrometry ( MS / MS )] and urine [gas chromatography ( GC ) MS ]. Serum acylcarnitines and urine organic acid profiles (n = 7) were determined for SPM horses. Results Seeds from box elder trees ( A cer negundo ) were present on all SPM and 61% of control pastures. Hypoglycin A , known to cause acquired multiple acyl‐ C o A dehydrogenase deficiency ( MADD ), was found in box elder seeds. Serum acylcarnitines and urine organic acid profiles in SPM horses were typical for MADD . The hypoglycin A metabolite methylenecyclopropylacetic acid ( MCPA ), known to be toxic in other species, was found in conjugated form in SPM horse serum and urine. Horses with SPM had longer turn‐out, more overgrazed pastures, and less supplemental feeding than control horses. Potential relevance For the first time, SPM has been linked to a toxin in seeds abundant on autumn pastures whose identified metabolite, MCPA , is known to cause acquired MADD , the pathological mechanism behind SPM and AM . Further research is required to determine the lethal dose of hypoglycin A in horses, as well as factors that affect annual seed burden and hypoglycin A content in A cer species in N orth A merica and E urope.