Chickens were traditionally machines to convert agrarian debris (bugs, seeds) into protein-rich eggs. Their current battery-farming use turning corn feed into breast, thigh, and wing meat is relatively novel.

Pigs are traditionally a way to convert farm waste and forest forage (grubs, mushrooms, nuts) into fat and protein, with pigs hardy enough to stand up to the forest's threats

Cows turn grassland forage into protein-rich milk, meat, and leather. Cows are sturdy enough to be turned loose to live freely outside of direct supervision for long periods in secured territory and then rounded up, so can be raised with little labor on large amounts of poor land. Can move long distances under own power, can be raised in remote areas and sold fresh in high-demand population centers. Dairy herds, by contrast, were kept right outside population centers. Quick-spoiling milk can be processed into cooking lipid butter and stable, transportable, marketable protein source cheese. Can be used as traction-generating and load-bearing beasts.

Sheep are similar to cows at smaller scale and requiring closer attention, process grassland into mutton, milk, and wool, once most important textile in world before cotton.

Horses convert grassland to service as traction-generating and load-bearing beasts. Intelligently trainable, nimblest animals practical to tide.

Donkeys convert grassland to service as traction-generating and load-bearing beasts. Size and output/consumption ratio makes more practical than horses for many applications, but intensely annoying.

Mules - we bred a donkey with a horse to make it less annoying.

Deer, Antelopes, Turkeys, Ducks, Pheasants, etc. - game animals. Sustain their own life cycle from undeveloped land, are hunted in regulated fashion to sustain stock.

Bees - plant-fertilizing function radically increases productivity of fields, yields rich, high-sugar, indefinitely stable honey

Doves - we used to fuckin' farm doves, we'd have big-ass birdhouses out in the fields. Not sure what that was about.

Ostriches - one of those 80s things, a tax dodgee that sounded cool on cocaine