Animal buildings
Animal buildings are the core of production on your farm - the chicken coop, pigsty, cowshed and the other stables turn milled feed into goods like eggs, milk, wool or pigs. On top of that, every animal building except the apiary drops manure into the silo as a by-product, so even a stable you put up for milk or wool earns its keep through manure too. They unlock one by one as your farm levels up, and each one eats a different feed milled from a different crop.
Animal buildings are worth putting up the moment your farm unlocks them, because you need manure all the time - whether you're currently collecting milk, wool or eggs. The only exception is the apiary, which works completely differently and gives no manure at all.
Every animal building makes a main good plus manure for the silo

All the stables on the main farm and the gourmet farm work on the same principle. You load feed made in the windmill into the building, wait out the production time and get the main good - eggs, milk, pigs, wool or donkeys - and along with it manure, which goes straight into the silo. I treat the manure as a bonus that piles up almost for free next to whatever main good I actually need.
That's exactly why it pays not to leave an animal building idle even when you don't need milk or wool right now - you'll put its manure to use elsewhere on the farm.
Nine animal buildings are split between three farms
Animal buildings unlock one by one as your farm level rises, and each of them belongs on a different farm.
| Building | Farm | Unlocks at level | Build cost | Workers | Main product |
|---|---|---|---|---|---|
| Chicken coop | Main farm | 0 | 1500 Dollars | 5 | Eggs |
| Pigsty | Main farm | 7 | 2000 Dollars | 4 | Pigs |
| Cowshed | Main farm | 13 | 8000 Dollars | 6 | Milk |
| Sheep pen | Main farm | 17 | 2000 Dollars | 4 | Raw wool |
| Goat stable | Gourmet farm | 19 | 40000 Dollars | 5 | Milk |
| Duck coop | Gourmet farm | 26 | 70000 Dollars | 5 | Eggs |
| Rabbit hutch | Gourmet farm | 28 | 150000 Dollars | 5 | Angora wool |
| Donkey stable | Gourmet farm | 28 | 150000 Dollars | 5 | Donkeys |
| Apiary | Flower farm | 56 | 240000 Dollars | 13 | Honey and wax |
Each animal gets feed milled from a different crop

You don't make the feed in the stable itself, but in the windmill or the water mill from a specific crop that you have to grow in a field first.
- Chicken coop - chicken feed is milled from corn
- Pigsty - pig feed is milled from cabbage or turnips
- Cowshed - cow feed is milled from wheat or alfalfa
- Sheep pen - the feed is milled from oats or meadow flowers
- Goat stable - the feed is milled from dandelions in the water mill
- Duck coop - the feed is milled from lamb's lettuce in the water mill
- Rabbit hutch - the feed is milled from parsnips in the water mill
- Donkey stable - the feed is milled from barley in the water mill
Before you expand or upgrade an animal building, it pays to check whether you have enough fields sown with that crop and enough free mills - otherwise the stable stays empty, because there'll be nothing to load into it.
Manure keeps even the orchards at the other end of the farm going

The manure tipped into the silo is processed further into fertilizer, which the orchards at the end of the production cycle need - the ones where you collect apples, cherries or other fruit and the fallen leaves for the composter. So a seemingly unrelated part of the farm depends directly on how many animal buildings you have running and how often you stock them with feed.
That's why I've found it works to keep several animal buildings going at once, even when I'm not collecting their main goods at full tilt - their manure ends up where it's needed anyway.
The apiary works completely differently from the other animal buildings

The apiary on the flower farm differs from the other stables in one fundamental way. Instead of feed from a mill it consumes nectar produced by the orchards on the same farm, and instead of eggs, milk or wool it gives honey and wax. You get no manure from it at all, so only the remaining eight animal buildings contribute to the silo.
Buildings and products mentioned in the text
Chicken coopMain farm · 5 × 5
PigstyMain farm · from level 7 · 7 × 6
CowshedMain farm · from level 13 · 8 × 5
Goat stableGourmet farm · from level 19 · 6 × 6
Duck coopGourmet farm · from level 26 · 8 × 6
Donkey stableGourmet farm · from level 28 · 8 × 7
ApiaryFlower farm · from level 56 · 11 × 6
Sheep penMain farm · from level 17 · 7 × 5