I don't know, however, what I've always thought to be true in dogs, is "that is when they are hungry enough, they will eat" The more you try to get a dog to eat, the more picky the little one will become. Especially a yorkie. Because these are very clever little dogs. Soon they have YOU trained.
IMO , though . Suzi, is a little more this way sometimes with her kibble, but, she eats when she wats to. I free feed her. Then I also give her canned foor, that is higher in protein. It is the same brand as her kibble, and is rated a 6 on the rating scale. She loves it too. I feed it to her once a day , and she does great on it. There is an organic type too.