Yup, hay can be high in sugars/carbs depending on when it was cut, the weather at the time, etc.
Soaking is a great way to make hay safer for foundering ponies - Put a biscuit or flake in a container of water big enough to cover it completely and leave it for an hour. The water turns a mucky molasses colour because of all the sugar that leaches out.
She is exactly right. If you are feeding alfalfa cut it back to a handfull a day, and soak that timothy or whatever grass hay. www.safegrass.org
Is a good place to start about foundered horses Kathy Watts. There is a pelleted feed for foundered horses Remedy, or Remission or something like that, I can look it up. Max. 1 hour a day on that pasture, you can keep lamititis at bay , but it takes a lot of effort, sorry to hear this news, have you checked for rotation yet Is it a confirmed Founder , or lami ? Founder being a rotation of the coffin bone , and the other the inflamation the tissue connecting the coffin bone to the hoof wall. I just read your above post , so if he has rotated 2 times its pretty serious. You can get some great info on hoof care at www.horseshoes.com
its a farrier forum, and its worth its weight in gold. You will learn a lot about making that pony as comfortable as possible barefoot or with corrective pads, depending on the x-rays. Remission is the name of that feed ,I am sure of it , you can get it in the US but not in Europe. I would stick to grass hay , soaked with added minerals , and a feed for foundered ponys like remission. Good luck.