So, Gen 1:29-30, God tells the man & the woman that he's given them all the green plants to eat, and furthermore that to every beast, bird, and creeping thing, "I have given every green plant for food." So absolutely every animal is vegetarian by divine fiat at creation.1 It's not until after the Flood that people (and animals, presumably) are allowed to eat meat: "[J]ust as I gave you the green plants, I give you everything" (Gen 9:3).2
But! What the hell is Abel up to? Abel is a shepherd, while his older brother Cain is a farmer. They each bring offerings to God, "Cain brought to the LORD an offering of the fruit of the ground, and Abel for his part brought the firstlings of his flock, their fat portions" (Gen 4:3-4). People aren't eating meat yet, so what's Abel doing herding sheep in the first place? Maybe it's just for the wool, but then, he kills some of them and cuts off the fatty bits to burn on an altar to God. How does he know how to slaughter and prepare them?
I guess, at the beginning of time, only God eats flesh.
1 Vegetarian or vegan? Probably no eggs, of course - they aren't green plants - but what about honey? Are the bees at least allowed to eat their own honey?
2 Everything? So there's no kosher laws yet, even though God tells Noah to take "seven pairs of all clean animals . . . and a pair of the animals that are not clean" (Gen 7:2).
