Genesis 30:37-39

37Jacob, however, took fresh-cut branches from poplar, almond and plane trees and made white stripes on them by peeling the bark and exposing the white inner wood of the branches.

38Then he placed the peeled branches in all the watering troughs, so that they would be directly in front of the flocks when they came to drink. When the flocks were in heat and came to drink,

39they mated in front of the branches. And they bore young that were streaked or speckled or spotted.