Then God said, “I give you every seed-bearing plant on the face of the whole earth and every tree that has fruit with seed in it. They will be yours for food. And to all the beasts of the earth and all the birds of the air and all the creatures that move on the ground—everything that has the breath of life in it—I give every green plant for food.” And it was so. Genesis 1:29-30

According to this verse at the beginning of the Bible, it appears animals were vegetarians. This explains why there wasn’t chaos onboard Noah’s ark! They all wanted a salad, not each other.

But things changed, it appears after the ark and the flood.

Then God blessed Noah and his sons, saying to them, “Be fruitful and increase in number and fill the earth. The fear and dread of you will fall upon all the beasts of the earth and all the birds of the air, upon every creature that moves along the ground, and upon all the fish of the sea; they are given into your hands. Everything that lives and moves will be food for you. Just as I gave you the green plants, I now give you everything.

“But you must not eat meat that has its lifeblood still in it. And for your lifeblood I will surely demand an accounting. I will demand an accounting from every animal. And from each man, too, I will demand an accounting for the life of his fellow man.” Genesis 9:1-5

• God tells man to eat animals.
• Animals will fear man, probably because man will acquire a taste for them.
• Man must not eat the meat raw, hinting at ancient Pagan practices.
• Every man and animal must account for the life they have taken.

This is the first time we see that animals will eat other animals. All this to say, when God restores the earth back to its original state, establishing a new heaven and a new earth, animals will probably once again eat vegetables and fruit.