Is Cat is a omnivorous?

Well, cats are obligate carnivores, meaning that they need to eat meat to survive. There are a number of reasons why cats don't do well on a vegan diet, but it all essentially comes down to this: they aren't adapted to it.

Why are cats carnivores?

Cats have the shortest digestive tract to body size ratio of any mammal. As a result, they have less fermenting bacteria to help them break down plant material and derive nutrients from it. For this and other reasons, cats are career carnivores that need to be kept on a meat-based diet.