Very interesting!
So is your old pony! Are you doing the treatment for the Cushings also? Has it been successful? I attended at friend's Cushings horse when he was put down. He was beginning to founder. The treatments hadn't really been working. I don't think my friend thought he would ever recover. And yet, it sounds like you've been through this a few times!
Unfortunately yes, I have more experience with this than I ever wanted. The pony is between 25 and 30 and no, I haven't started him on the pergolide just yet. He really doesn't appear to be sick at all, except for his long, furry coat year 'round and the founder problem. I body clip him in summer and try to manage the founder the best I can. I'll start pergolide if he starts to really get sick but he will eventually have to be put down.