Genesis 30:37-39

Jacob, however, cut green branches of poplar, almond, and plane trees and peeled back part of their bark, to expose the white inner wood of the branches. Then he set the partially peeled branches inside the water troughs where the goats would see them when they came to drink. For they mated when they came to the water troughs, and as they lowered their heads to drink, they saw the stripped branches in front of their eyes. Miraculously they gave birth to streaked, speckled, and spotted young.