Livestock Pens are buildings that train Sheep. With a Home City Card, the Livestock Pen can also train Cows. Sheep are very useful as a source of Food, fattening as time goes on. While confined within livestock pens Sheep, Llamas, and Cows fatten at a much faster rate.
"Keeping animals was important to the founding of the New World, especially as areas became settled and hunting became less abundant. Animals were used for food, but they had other uses as well. Fat from animals was used to make soap, the skins were used for clothing, and tallow was used in candles. Tallow was also used to keep leather supple and water-resistant."