Genesis 30:37-39

37Then Jacob took branches of fresh poplar and almond and plane trees, and peeled white stripes in them, exposing the white in the branches.

38Then 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.

39So the flocks mated and conceived by the branches, and the flocks gave birth to streaked, speckled, and spotted offspring.