The introduction of certain animals from Europe, especially horses, had a positive effect on some American Indian communities. However, European cattle and other livestock sometimes caused more harm than good. In some cases, livestock entered the unfenced fields of American Indian farmers, eating and trampling their crops. Unlike European farmers, many American Indian farmers had never learned how to fence in their fields because it had never been necessary. The American Indians in the Spanish colony of New Spain in Central and North America experienced this problem. Antonio de Mendoza, the first viceroy of New Spain, wrote these words to the Spanish king in the 1530s:

May your Lordship realize that if cattle are allowed, the Indians will be destroyed.

How could the Spanish have helped American Indians adapt to the new species of livestock?