Interesting. The way the old formula is described, it appears that it contains more meat than the new. The new appears to contain too much bone -- chicken necks are pretty much all bone with a small amount of meat; chicken backs are all bone. This is just an observation from the company's description. It could be that the meat used in the old formula is just better described in the new one.And as far as the change in formula is concerned.....here is the change in the meat portion:
Old: Chicken meat (inc. bone), chicken gizzards, chicken livers, chicken hearts; 15% crude protein, 6% crude fat.
New: Chicken Necks with ground bone, Chicken Backs, Chicken Thigh Meat, Chicken Gizzards, Chicken Livers, Chicken Hearts; 16% crude protein, 11% crude fat.
Without knowing the exact percentages of meat to bone in either formula, it's possible that the new formula contains too much calcium in the form of bone and not enough protein in the form of meat.