In case you haven't sorted this out, I would be very concerned about feeding this hay. It burned your skin and gave your horses diarrhea. Sugar and minerals don't mean a thing if you have a hay that is either physically irritating or actually toxic. I would put them on something safe while I figured out what to do. If you already own the hay, you would do well do find out what is going on or ask the seller to take it back due to the extreme problems.
Good luck and hang in there!
Bucks Co., PA