Just want to add in another opinion...
I would not put any yorkie on a high protein diet unless they had been Bile Acid Tested first.... yorkies are so prone to liver disease and many MVD dogs do not show signs until later in life. I had one of my yorkies on a grain free/high protein diet before I found out about his MVD and now I could kick myself for the time he was on it.
So if you are considering grain free/high protein foods which can be very beneficial for some dogs... I suggest you have BATs done first