Why are Cats & Dogs different ?
Why are Cats so different from Dogs - Nutritionally Speaking?

The principal reason that cats have dietary needs that differ from dogs is because they are obligate carnivores. They have been eating mainly animal tissue for a very long time, some 30 million years at least!  Over that enormously long period of time, cats have evolved in such a way that they absolutely must dine on other animals as the major part of their diet. This requirement is so strongly built in to cats that there is no possibility that we can in any practical sense, turn our cats into vegetarians.

The cat has lost the ability to utilise or cannot convert a range of nutrients (found in vegetable material) into a number of essential nutrients found only in animal tissue.   And I have mentioned one already, the case of beta-carotene and vitamin A.

However, this is good news not bad

What this means, is that cats, being obligate carnivores,   have very simple dietary needs. For example, your cat could live its whole life on a steady diet of mice and be perfectly healthy - assuming of course those mice did not pass on some form of parasite such as Toxoplasmosis to your cat.
BIOLOGICALLY APPROPRIATE RAW FOOD Diet