Hypoglycin A in maple trees in the Netherlands and the risk of equine atypical myopathy

The Acer (maple) genus of trees comprises over 120 species worldwide. Some of these contain the plant-toxin hypoglycin-A which has been proven to be a cause of the highly fatal condition called atypical myopathy (AM) in horses and ponies. In an earlier study of maple-tree samples (leaves and seeds) collected by owners of healthy and AM-affected horses it was shown that the seeds contain significantly more toxin than the leaves. There is a concern as to whether maple trees can be safely retained or planted around paddocks or pastures, and whether there is a difference in toxicity between different species. The aim of the present study was to investigate the amount of toxin in different maple-tree species present in The Netherlands. The seeds of 20 different tree-species of the ‘Acer’ genus, present in the arboretum in Wageningen, The Netherlands, were analysed for hypoglycin-A; 8 species belonged to the ‘Platanoidea’ subgenus (section), 7 to the ‘Acer’, 3 to the ‘Palmata’ and 2 to the ‘Negundo’ subgenera. Assay was carried out using a newly validated method based on liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Seeds of the maple trees belonging to the ‘Platanoidea’ contained no hypoglycin-A. The seeds of species belonging to the ‘Acer’, ‘Palmata’ and ‘Negundo’ subgenera however contained 96– 1744 mg/kg, 4–32 mg/kg and 3–444 mg/kg of the toxin respectively. These results indicate that the precise tree species is an important aspect when giving advice regarding the toxicity of maple trees and the consequent risk for horses.