Horses in Agriculture (gallery)

Horses played a pivotal role in the agricultural transformation of the United States in the nineteenth and early twentieth centuries. This gallery illustrates how new mechanical systems in agriculture evolved around horses and deployed them for tasks such as reaping and harvesting. The gallery demonstrates how horses remained an enduring feature in American agriculture during a period of rapid technological change. 

Why do you think horses remained pivotal for agriculture for such a long period of time? What advantages did horses offer that might explain their persistence, and even growth, as a source of agricultural power?