Potential new sources of hypoglycin A poisoning for equids kept at pasture in spring: a field pilot study

Abstract

Equine atypical myopathy in Europe results from hypoglycin A (HGA) exposure through the ingestion of samaras or seedlings of the sycamore maple tree. This pilot study aimed at better defining sources of HGA intoxication in spring. Samaras fallen on the ground and then seedlings were collected at two-week intervals from sycamore, Norway, and field maple trees over the spring 2016. In early April, rainwater from wet seedlings collected after a rainy night was harvested to be analysed. Mid-May, samaras of the box elder, common ash, and inflorescences of sycamore maples were collected on the tree. Quantification of HGA in samples was performed using high performance thin layer chromatography. Hypoglycin A was detected in all samples from sycamore including rainwater but tested negative for Norway, field maples. The samaras of the box elder found in the present study area did not contain a seed within their husk and thus tested negative. From the maximum HGA concentrations found, it may be extrapolated that at some periods and locations, about 20 g of samaras, 50 seedlings, 150 g of inforescences or 2 liters of water that has been in contact with seedlings would contain the maximum tolerated dose per day for a horse.

Answers to the Frequently Asked Questions Regarding Horse Feeding and Management Practices to Reduce the Risk of Atypical Myopathy

“…When in doubt, professional expertise should be sought to identify the tree (botanists and/or forestry agents might be of help). Recently, it has been suggested that flowers falling from sycamore trees after heavy rainfall and/or wind could be an additional source of intoxication [26].…”

“…However, when samaras are too abundant and/or too widely dispersed within the premise, grazing in the affected area must be prohibited. Another way to limit grazing to areas free of fallen seeds and/or flowers and/or seedlings is to create parcels within the pasture [26].…”

“…Furthermore, humid pastures are of particular risk for AM and grazing should therefore also be avoided on these pastures [17]. HGA is a water-soluble toxin that may pass from plants to water by direct contact [26,30]. This solubility might explain the risk associated with humidity and the protective factor linked to drinking water provided via the distribution network.…”

“…Up to now, not a single case of our database has been confirmed in horses that had no access to pasture and/or paddock based on HGA and MCPA-carnitine detection (unpublished data). Thus, it is advised to stable horses during autumn and spring outbreaks if seeds or seedlings are, or may be, present at pasture [26]. However, keeping a horse in the stable day and night may be difficult and is not considered as good practice in animal welfare [31,32].…”

“…Regarding spring outbreaks, horse owners wonder if the case series stops because the seedlings have lost in toxicity. Actually, the end of spring outbreaks may not be explained by the disappearance of the toxicity since the seedlings remain toxic [26]. It is however hypothesized that spring outbreaks cease following a relative decrease in risk of intoxication by grazing.…”