Genesis 30:37-39

37Jacob, however, took fresh branches of poplar, almond, and plane trees, and peeled the bark, exposing the white inner wood of the branches. 38Then he set the peeled branches in the watering troughs in front of the flocks coming in to drink. So 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.