Isaiah 65:25 (RSV):

The wolf and the lamb shall feed together, the lion shall eat straw like the ox; and dust shall be the serpent’s food. They shall not hurt or destroy in all my holy mountain, says the LORD.

Vegans are right. But they are too early. One name for this is an over-realized eschatology. In the terminology of New Testament theology, they have too much “already” and not enough “not yet”. But one day, the physiology of even the most carnivorous of animals will turn to eating straw fiber. But that day is not yet. Even feed a cat a vegan diet and it would eventually die of malnourishment.