Genesis 30:38-42

He set the rods which he had peeled in front of the flocks in the drinking troughs, that is, in the watering channels where the flocks came to drink; and they mated when they came to drink.

So the flocks mated by the rods, and the flocks delivered striped, speckled, and spotted offspring.

Then Jacob separated the lambs, and made the flocks face toward the striped and all the black in the flock of Laban; and he put his own herds apart, and did not put them with Laban’s flock.

Moreover, whenever the stronger of the flock were mating, Jacob would place the rods in the sight of the flock in the drinking troughs, so that they would mate by the rods;

but when the flock was sickly, he did not put them in; so the sickly were Laban’s, and the stronger were Jacob’s.