The coop side
Chickens (50g eggs, more if golden through petting and friendship) are the cheapest animal and pay back the 800g coop quickly, especially with mayo makers doubling egg value. Ducks lay every other day for 240g (350g as mayo) and rabbits drop wool plus 1–2 rabbit feet — the most valuable coop product per animal but slow to start.
The barn side
Cows milk daily for 125g (190g as cheese, more if gold quality) — cheese is the barn’s bread and butter. Goats milk every other day for 225g (400g as goat cheese). Pigs are the endgame: truffles daily once mature, worth 625g raw and up to 1,491g as truffle oil, but they only forage outdoors on non-rain days and need fence-free space to work.
The routine that multiplies income
Pet every animal daily (+friendship), leave the door open on sunny days for free forage happiness, and process everything: eggs to mayo, milk to cheese, wool stays raw or goes to the loom. Hearty processing doubles or triples base prices — a barn of happy cows is effectively a cheese factory.