Atypical myopathy can be associated with the ingestion of sycamore samaras and also ingestion of seedlings. Hypoglycin A can be detected in the blood of horses with no detectable clinical signs at pasture in which there is A. pseudoplatanus. Determination of hypoglycin A concentration in blood is useful for screening for exposure in suspected cases of AM.

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Sycamore and box elder trees in New Zealand are a source of hypoglycin A associated with the development of atypical myopathy. If pastured horses present with clinical and biochemical signs of severe muscle damage then the environment should be checked for the presence of these trees. Horses should be prevented from grazing samaras from Acer spp. in the autumn.

26Hypoglycin A (HGA) is a toxin contained in seeds of the sycamore maple tree (Acer pseudoplatanus). Ingestion of this 27 amino acid causes equine atypical myopathy (AM) in Europe. Another variety, A. negundo, is claimed to be present 28where AM cases were reported in the US. For unknown reasons, occurrence of this disease has increased. It is 29 important to define environmental key factors that may influence toxicity of samaras from Acer species. In addition, the 30 content of HGA in seedlings needs to be determined since AM outbreaks, during autumn period when the seeds fall but 31 also during spring when seeds are germinating. The present study aims to validate a reliable method using high 32 performance thin layer chromatography for determination and comparison of HGA in samaras and seedlings. 33The working range of the method was between 20 µg HGA to 408 µg HGA per ml water, corresponding to 12 -244 34 mg/kg fresh weight or 40 -816 mg/kg dry weight, taking into account of an arbitrary average dry matter content of 35 30%. Instrumental limit of detection and limit of quantification were of 10 µg HGA/ml and 20 µg HGA/ml water, 41They also suggest that detected levels of HGA are highly variable. This confirmed the suitability of the method for 42HGA detection in samaras or seedling. 43

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