Cow is the animal a survival world quietly runs on. Beef feeds you, and leather is the input for books, bookshelves, item frames and armour — which makes a cow farm a prerequisite for an enchanting setup long before it is a food supply.
Wheat is the answer to what cows eat, to how they breed and to how you move them. Two adults fed wheat pair off and produce a calf; any Cow within a few blocks follows a player holding wheat, which is how a herd walks itself into a cow pen without a single lead; and feeding a calf wheat shortens the wait before it grows up.
An empty bucket used on a Cow fills with milk, and milk is the game's eraser: drinking it clears every status effect at once, the good with the bad. That makes it the cure for poison, the mistake that wipes your own potion buffs, and the ingredient a cake cannot be made without.
Cows come in climate variants. A warm Cow lives in deserts, savannas, jungles and badlands, a cold Cow with a shaggy coat and forward-pointing horns lives in taigas and windswept hills, and the plain temperate one fills everything in between. The mooshroom of the mushroom fields is a further variant again: shear it and it drops mushrooms and turns into an ordinary Cow for good, and it will not breed with one.