DESCRIPTIVE CLINICAL REPORT
Seasonal pasture myopathy/atypical myopathy in North America associated with ingestion of hypoglycin A within seeds of the box elder tree
Article first published online: 20 NOV 2012
© 2012 EVJ Ltd
Equine Veterinary Journal
Volume 45, Issue 4, pages 419–426, July 2013
How to Cite
Valberg, S. J., Sponseller, B. T., Hegeman, A. D., Earing, J., Bender, J. B., Martinson, K. L., Patterson, S. E. and Sweetman, L. (2013), Seasonal pasture myopathy/atypical myopathy in North America associated with ingestion of hypoglycin A within seeds of the box elder tree. Equine Veterinary Journal, 45: 419–426. doi: 10.1111/j.2042-3306.2012.00684.x
- Issue published online: 6 JUN 2013
- Article first published online: 20 NOV 2012
- Accepted manuscript online: 28 SEP 2012 05:45AM EST
- Manuscript Accepted: 21 SEP 2012
- Manuscript Received: 17 JUL 2012
- Rapid Agricultural Response Fund
- beta oxidation;
- multiple acyl-coA dehydrogenase
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.
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.
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.
Seeds from box elder trees (Acer negundo) were present on all SPM and 61% of control pastures. Hypoglycin A, known to cause acquired multiple acyl-CoA 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.
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 Acer species in North America and Europe.