a friend of mine had to deal with this and she had a little pony that liver out he was quite young and was euthonised [sorry spelling lol] im sure before treatment as unfortunatly but discustingly had no insurance so not sure whether treatment would have worked.i expect you know then but this may help others to find suitable grazing that a few years ago americans first discovered [maybe wrong]that if any building work has took place around the said grazed areas that in future years it will cause grass sickness in horses and ponies.i do still believe that theory as alot of places were knocked down and rebuilt just yards from this field where the said horse died.funny enough no one had heard of this when i spoke bout it but i actuslly learnrd a hell of alot just from veterinary books as i was looking in2 going into that line of work and wanted to learn as much as poss first..hope it helped slightly soz couldnt be more helpful