Genesis 30:37-42

37But Jacob took fresh-cut branches from poplar, almond, and plane trees. He made white streaks by peeling them, making the white inner wood in the branches visible.

38Then he set up the peeled branches in all the watering troughs where the flocks came to drink. He set up the branches in front of the flocks when they were in heat and came to drink.

39When the sheep mated in front of the branches, they gave birth to young that were streaked or speckled or spotted.

40Jacob removed these lambs, but he made the rest of the flock face the streaked and completely dark-colored animals in Laban’s flock. So he made separate flocks for himself and did not mix them with Laban’s flocks.

41When the stronger females were in heat, Jacob would set up the branches in the troughs in front of the flock, so they would mate near the branches.

42But if the animals were weaker, he did not set the branches there. So the weaker animals ended up belonging to Laban and the stronger animals to Jacob.