Genesis 30:37-39

Then Jacob took branches of fresh poplar and almond and plane trees, and peeled white stripes in them, exposing the white in the branches. Then he set the branches which he had peeled in front of the flocks in the watering troughs, where the flocks came to drink; and they mated and conceived when they came to drink. So the flocks mated and conceived by the branches, and the flocks gave birth to streaked, speckled, and spotted offspring.