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72 h [2,5,6]. The cause(s) of SPM and AM are unknown;

however, proposed contributingfactorsincludelowdietaryselenium[4],ingestionofC. sordelli toxin in the soil [8] and ingestion of maple leaves (Acer pseudoplatanus) infested with European tar spot fungus (Rhytisma acerinum) [9]. White snakeroottoxicityhasalsobeenproposedbutappearsunlikelyafterfurther evaluation of cases in the Midwestern USA [2]. Horses with SPM and AM have a lipid storage myopathy involving oxidative postural and respiratory muscles and, in some cases, cardiac muscle [2,10]. Studies of AM and, subsequently, SPM identi?ed an acquired de?ciency in skeletal muscle multiple acyl-CoA dehydrogenases (MADD), which produces a speci?c abnormal pattern of accumulation of blood acylcarnitines and urine organic acids [11,12]. Inherited forms of MADD in man are due to mutations in the electron transfer ?avoprotein gene, the electron transfer ?avoproteinC dehydrogenase gene [13] and ribo?avin transporters [14]. Clinical signs range from a fatal neonatal condition to an adult onset mild lipid storage myopathy [15]. An acquired form of MADD also exists in man, arising from ingestion of seeds of the unripe Jamaican ackee fruit (Blighia sapida) [16,17]. Ackee seeds contain high concentrations of a nonproteogenic amino acid called hypoglycin A (L-a-amino-methylenecyclopropylpropionic acid) whose metabolite methylenecyclopropylacetic acid (MCPA) is metabolised to MCPA-CoA, which is a potent inhibitor of multiple acyl-CoA dehydrogenases [17]. Ingestion of unripe ackee fruit can be lethal in man, with clinical signs of hypoglycaemia and persistent vomiting [16,17]. Hypoglycin A has also been found in seeds from a tree species, Acer, common in the Midwestern USA, which is a member of the same Sapindaceae family as Blighia sapida [18]. Acer spp. with black tar spot fungus on their leaves have been noted previously in pastures of horses with AM [9]. We hypothesised that SPM in horses was caused by ingestion of seeds plentifulinfallpasturesthatcontainedhighconcentrationsofhypoglycinA. The objectives of this study were to determine: 1) whether there was a common abundant seed-bearing plant in pastures of horses affected by SPM in the fall;

2) whether hypoglycin A was present in the fall burden of seeds from that plant;

and 3) whether toxic hypoglycin metabolites could be identi?ed in serum or urine from affected horses. bs_bs_banner Equine Veterinary Journal ISSN 0425-1644 DOI: 10.1111/j.2042-3306.2012.00684.x

419 Equine Veterinary Journal

45 (2013) 419C426 ?

2012 EVJ Ltd Materials and methods Horses Seasonal pasture myopathy cases were identi?ed from muscle biopsy submissions to the Neuromuscular Diagnostic Laboratory at ........