Hi Christine,

This is indeed frustrating. You have obviously gone above and beyond to get to the bottom of the problem,especially with your specialization in equine body issues.
Please don't be cross if I return to something I suggested earlier. One is to try to find soy hull pellets,since they are safe and have not been tried. Cattle farmers use them,so if your equine feed store doesn't carry them,maybe a place selling cattle feed will. They are not hard like alfalfa pellets,but soft enough that just a sprinkle of water will cause them to start breaking down. So you could experiment with how little water to use in order for it not to be mushier than he likes. I only use a sprinkle of water because I worry about choke. But maybe unless a pony bolts his food it isn't an issue.
And many of us know that sometimes there's just no 'splaining what makes a pony decide what is poisonous and what  isn't. From one day to next.
And the second thing....please bear with me....is the idea of mechanical issues with his hooves. I am not a podiatrist,but to me his front feet look out of balance.
Slightly. And those of us who have had hoof issues( 5 of my then - 9 horses lost all of their hooves years ago)know how even a very small change in trim can make a world of difference. I am so interested to hear if others more experienced than am I have the same response.
Otherwise, just ignore me. 🤐
--
Lorna in Eastern Ontario
2002