And I don't pour the feed to them even after they have adjusted. I just let them gain their weight gradually, and feed them what I would feed a normal horse of size, age, etc. It takes longer.... and I'm always antsy to get them fat, but it just seems healthier that way.
I have found colic to be the biggest threat.
I'm sure I'm not saying anything you don't already know and again, what a blessing that you have found them.