Matthew Poole and continuators on Genesis 30:41

41 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.

It is known that the cattle in those parts did conceive and bring forth twice in a year, at spring and in Autumn; and it is supposed that the stronger here mentioned are such as joyned in the spring, and the feeble they that joyned in Autumn.