Genesis 30:37-39

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

38He set the sticks that he had peeled in front of the flocks in the troughs, that is, the watering places, where the flocks came to drink. And since they bred when they came to drink,

39the flocks bred in front of the sticks and so the flocks brought forth striped, speckled, and spotted.