Hi Steve, pet food companies include Chicken, eggs, fish in most cat food products with makes pets addicted to these proteins, hence, the creation of food allergy due to excess of the same protein in the animal diet. That’s how it works. For this reason, is convenient and reasonable to do rotational feeding to cats often to avoid this problem from happening. The idea is not to get stuck with the same protein in the same cat food for over a year. Chicken fat is not defined as a protein allergen, which is the cause of allergy in cats, the cat’s addiction to chicken protein, and refusing to eat any food which doesn’t contain it, creates the allergy, the same with any other type of animal protein or ingredients, like dairy. Even though chicken fat is processed, purified, and doesn’t contain protein, it could be a problem if you already have a high allergic-to-chicken cat. My suggestion for rotational feeding is a way to prevent cats from developing a chicken allergy, but the same goes for other types of proteins in excess over a prolonged period of time. Regarding formulas with high content of fish, I don’t generally recommend them since they are usually highly addictive to the cat’s palate which creates allergy faster than chicken, they are usually in forms of meal which eliminates the essential fatty acids they could provide and in general cause some urinary tract issues, especially in male cats.