Genesis 30:41-42

41Jacob waited until the stronger female animals were ready to have sex. Then he put the special branches in front of them, near the big bowls of water. Then these animals would see the branches when they had sex together.

42But if the female animals were weak, he did not put the branches in front of them when they had sex. As a result, the weak animals would belong to Laban, but Jacob would keep the strong animals.