Genesis 30:38

30:38 Then 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. ¹ 

Genesis 30:41

30:41 When the stronger females were in heat, ²  Jacob would set up the branches in the troughs in front of the flock, so they would mate near the branches.

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¹ sn He put the branches in front of the flocks…when they came to drink. It was generally believed that placing such “visual aids” before the animals as they were mating, it was possible to influence the appearance of their offspring. E. A. Speiser notes that “Jacob finds a way to outwit his father-in-law, through prenatal conditioning of the flock by visual aids – in conformance with universal folk beliefs” (Genesis [AB], 238). Nevertheless, in spite of Jacob’s efforts at animal husbandry, he still attributes the resulting success to God (see 31:5).

² tn Heb “and at every breeding-heat of the flock.”