Sorry you haven't gotten any responses. Have you tried to post this question in the health and diet section?
My dog would rather eat ANYONE'S food but his own...even though he loves his kibble. I think it's a competition thing for him though
Have you considered switching your puppy's food? What brand does your larger dog eat? Personally, I would not feed Iams to my dog, even thought your breeder recommended it. There are many healthier, high-quality foods that you can learn about in the health and diet section.