You may discover that your Animal population increases rapidly in Farmville, even if you never purchase an Animal from the Market. You can obtain a host of Animals by virtue of the Lost Animals option as well as Gifts from Neighbours, Rewards for your accomplishments and Rewards for the accomplishments of your Neighbours.
A Chicken Coop can house up to 20 Chickens. A Dairy Barn can house up to 20 Cows and 1 Bull. A Stable can house up to 20 Horses and a temporary resident in the form of the Wandering Stallion. Where do all the Ducks, Geese, Llamas and sundry other Animals go?