Whenever the stronger females of the flock were in heat, Jacob would place the branches in the troughs, in full view of the animals, so that they would breed in front of the branches.
Here is Jacob's honest policy to make his bargain more advantageous to himself than it was likely to be. If he had not taken some course to help himself, it would have been a bad bargain indeed, which he knew Laban would never consider, or rather would be well pleased to see him a loser by, so little did Laban consult any one's interest but his own.
Commenting on Genesis 30:37-43
JACOB'S COVENANT WITH LABAN. (Gen. 30:25-43) when Rachel had born Joseph--Shortly after the birth of this son, Jacob's term of servitude expired, and feeling anxious to establish an independence for his family, he probably, from knowing that Esau was out of the way, announced his intention of returning to Canaan (Heb 13:14).
Commenting on Genesis 30:25-43
And it came to pass, whensoever the stronger cattle did conceive, that Jacob laid the rods before the eyes of the cattle in the gutters, that they might conceive among the rods. (m) As they which took the ram about September and brought forth about March: so the feebler in March and lamb in September.