Genesis 30:37-43

Then Jacob took some fresh branches from poplar, almond, and plane trees and peeled off strips of bark, making white streaks on them. Then he placed these peeled branches in the watering troughs where the flocks came to drink, for that was where they mated. And when they mated in front of the white-streaked branches, they gave birth to young that were streaked, speckled, and spotted. Jacob separated those lambs from Laban’s flock. And at mating time he turned the flock to face Laban’s animals that were streaked or black. This is how he built his own flock instead of increasing Laban’s. Whenever the stronger females were ready to mate, Jacob would place the peeled branches in the watering troughs in front of them. Then they would mate in front of the branches. But he didn’t do this with the weaker ones, so the weaker lambs belonged to Laban, and the stronger ones were Jacob’s. As a result, Jacob became very wealthy, with large flocks of sheep and goats, female and male servants, and many camels and donkeys.