I have a vegan cat. He can't live without grass, eats it every day like a sheep. Besides, he digests it well. He doesn't eat meat at all! It surprises me a lot, of course. He also loves grapes, but then I found out cats don't have enzymes to digest sugar. This can lead to diabetes, so you should refrain from giving it too many sweets. Interestingly enough, grapes are great for guinea pigs, I found this out in an article - https://pawbility.com/can-guinea-pigs-eat-grapes/. As it turns out, this food is a great source of healthy essentials for guineas. So, in addition to oats and bran, I often feed her a grape or two.