Atypical myopathy-associated hypoglycin A toxin remains in sycamore seedlings despite mowing, herbicidal spraying or storage in hay and silage.

Abstract

Several pasture management strategies have been proposed to avoid hypoglycin A (HGA) intoxication in horses, but their efficacy has never been investigated. To evaluate the effect of mowing and herbicidal spraying on HGA content of sycamore seedlings and the presence of HGA in seeds and seedlings processed within haylage and silage. Experimental study. Groups of seedlings were mowed (n=6), sprayed with a dimethylamine-based (n=2) or a picolinic acid-based herbicide (n=1). Seedlings were collected before intervention, and at 48h, 1 and 2weeks after. Cut grass in the vicinity of mowed seedlings was collected pre-cutting and after 1week. Seeds and seedling (n=6) samples processed within haylage and silage were collected. HGA concentration in samples was measured using a validated LC-MS-based method. There was no significant decline in HGA content in either mowed or sprayed seedlings; indeed, mowing induced a temporary significant rise in HGA content of seedlings. HGA concentration increased significantly (albeit to low levels) in grass cut with the seedlings by 1week. HGA was still present in sycamore material after 6-8months storage within either hay or silage. Restricted number of herbicide compounds tested. Neither mowing nor herbicidal spraying reduces HGA concentration in sycamore seedlings up to 2weeks after intervention. Cross contamination is possible between grass and sycamore seedlings when mowed together. Mowing followed by collection of sycamore seedlings seems the current best option to avoid HGA toxicity in horses grazing contaminated pasture. Pastures contaminated with sycamore material should not be used to produce processed hay or silage as both seedlings and seeds present in the bales still pose a risk of intoxication.