After a number of turns, the food type units will depop and related rations will appear in the larder of the nearest city and/or the capital. LIAB Prologue 15 In the case of pigs, it's goods like bacon, and for chickens it's plucked hens good for stewing.
Farms are unique because they are the only places where these food-type units can pop and depop, mimicking Stupidworld life-cycles. Piglets grow into pigs, then depop. Chickens lay eggs for ten turns, then lay a special "fertile" egg, and after three turns when the chick pops the mother hen depops, becoming a plucked chicken. The chick then grows for three turns before becoming an egg-laying hen.Hvs.tCF 123 Chickens, fertile eggs, and presumably pigs and piglets do not undergo this cycle if taken outside of a Farm.
However, breaking or stealing a fertile egg will continuously reset a hen back to laying normal eggs, effectively making it immortal.
Farms benefit from having a unit supervise, which increases production.Hvs.tCF 123