What's the calcium % of natures domain? The max percentage, not the min... does it say it on the bag? That's a grain free, right? There aren't many grain frees out there that i'd feed to a puppy because of the amount of calcium.
And if he currently doesn't like what he's on... find something else. Iams is not one of the better options out there. Just search around here about what to feed a puppy and you'll get plenty of good opinions.
If you don't want to feed a LBP formula, find an appropriate adult formula. I never fed a puppy food to my current dog. Probably won't with the next one either.