Cow & Bull

Cows are common domestic animals, which can be traded for in many villages. They are one of the few animals that can be milked, and can be butchered like other animals for fat and meat. They are very good at carrying objects, and can carry over 100 lbs. A cow in v3.17 costs 137 arrows.

Bulls
The male version of cows. They are almost always sold in villages which sell cows. They cannot be milked (obviously), and carry the same weight. (pre 3.15)

(3.15) Bulls can carry 273 lb. making them useful pack animals for trading trips.