But when the cattle were feeble, he put them not in: so the feebler were Laban's, and the stronger Jacob's.
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George Leo Haydock
Later-coming, in autumn, when the spring lambs were of an inferior value. These he was willing to abandon for the most part to Laban; and therefore did not use his rods. Pliny, Natural History viii. 47; and Columella viii. 3, agree, that the lambs which are produced in spring, do not thrive so well as those of autumn, at least in Italy, and in those countries where sheep lamb twice a year. Bis gravidæ pecudes. (Virgil) (Calmet)
Many who have tried the same experiment as Jacob, have not experienced the same success; whence St. Chrysostom, and most of the Greek fathers, suppose that it was miraculous. (Tirinus)