Initially at least, the Columbian exchange of animals largely went in one direction, from Europe to the New World, as the Eurasian regions had domesticated many more animals. Horses, donkeys, mules, pigs, cattle, sheep, goats, chickens, large dogs, cats, and bees were rapidly adopted by native peoples for transport, food, and other uses. One of the first European exports to the Americas, the horse, changed the lives of many Native American tribes. The mountain tribes shifted to a nomadic lifestyle, based on hunting bison on horseback. They largely gave up settled agriculture. Horse culture was adopted gradually by Great Plains Indians. The existing Plains tribes expanded their territories with horses, and the animals were considered so valuable that horse herds became a measure of wealth.