Hi Tom-
Something that the breeder may or may not (but should have mentioned) is that anytime you bring home a new puppy it is important that they stay on the same food the breeder had them on for 3-4 weeks before doing a slow transition to a new diet. This is to prevent the issue you are having. Moving is stressful for them and stress coupled with a food switch (even though you did it over 10 days) can cause GI distress.
It sounds like they were doing best on Iams large breed puppy. This is what I would have them on. The itching could be a coincidence or perhaps they had a couple fleas that you never saw. It is almost a slim to none chance that they BOTH are itching due to a food allergy. Not much logic there.
Merrick has no food appropriate for a large breed puppy last I knew and the only thing I know about Life’s Abundance is that their sales reps are very annoying and the main reason breeders use the food is because they make a profit off it. It’s nothing special.
If you truly do not want them back on Iams because of the dull coats, I would try Pro Plan Focus Large Breed Puppy. My dogs have beautiful coats on Pro Plan, stool is perfect and the food is highly digestable.
