Seasonal pasture myopathy/atypical myopathy in North America associated with ingestion of hypoglycin A within seeds of the box elder tree.

The research article presents a study that links the seasonal pasture myopathy (SPM), a horse disease, to the intake of hypoglycin A from the seeds of box elder trees, which becomes abundant during autumn. The toxic action of this amino acid seems to operate via a mechanism known as acquired multiple acyl-CoA dehydrogenase deficiency (MADD).

Objective and Methodology

The researchers aimed to identify a seed-bearing plant common in the autumn pastures of horses showing signs of seasonal pasture myopathy (SPM), which heavily mirrors the symptoms of atypical myopathy (AM). They also sought to confirm whether the SPM condition was the result of consuming the toxic amino acid hypoglycin A found in these plants.

• Twelve instances of SPM were studied with additional visits to 11 SPM pastures and 23 control farms. The purpose was to find a plant common to all these locations during the autumn season.
• A widely occurring seed from these visits was tested for its amino acid profile using gas chromatography-mass spectrometry (GC-MS) to check for the presence of hypoglycin A.
• The serum and urine samples from the horses were also examined, looking for the metabolite of hypoglycin A, specifically in its conjugated form.
• The researchers also explored the serum acylcarnitines and urine organic acid profiles of SPM-affected horses.

Results

• The researchers identified seeds from box elder trees (Acer negundo) in all SPM and 61% of control pastures.
• Hypoglycin A, known to cause MADD disorder, was discovered in box elder seeds. Thus, the ingestion of these seeds by horses potentially linked the cause of SPM and AM to this specific amino acid.
• The serum acylcarnitines and urine organic acid profiles in SPM horses were found to be typical to instances of MADD, reinforcing the link.
• The metabolite of hypoglycin A, 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 common conditions such as longer turn-out, overgrazed pastures, and less supplemental feeding compared to control horses.

Conclusions

The research, for the first time, links the condition of SPM to a toxin (hypoglycin A) in box elder seeds abundant in autumn pastures. The findings may serve as a critical ground for future research aimed at determining the lethal dose of hypoglycin A in horses, as well as the factors influencing the annual seed burden and hypoglycin A levels in Acer species across North America and Europe.