Keep trying! At that age, all of my dogs preferred canned food like Wellness. There is a puppy mousse made by Royal Canin that many like.
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I also had to hand feed the wet food for awhile to get them interested. It took them awhile to be interested in food from a bowl.
Small bits of shredded chicken may interest him.
Watch out with the nutrical. If you aren't following it up with a protein it can actually make the dog hypoglycemic.