I was always told you should slowly switch food. Gradually mixing in the new and reducing the old. Do this for at least 2 weeks but the longer the better. You might research adding canned pure pumpkin (libby's) not the pie filling and how much to add. Not sure for a yorkie size. I was told to give a little in my german shepherds foods when switching. But be careful with the amounts because different amounts will make it go either way too firm or too soft . I'm sure others here will be more knowledgeable about the yorkie size.
