What does the Pasuk mean when it writes that "Yakov set aside the lambs"?
Rashi and Rashbam 1 : He set aside all the spotted and blotched lambs and those that were reddish-brown (born in the first two years - Rashbam) which he then placed at the head of the flock (as the Pasuk goes on to explain) 2 , so that the sheep followed them and saw them constantly, until their image was implanted in their minds and when he they gave birth, they gave birth accordingly. The Rashbam points out that Yakov did this in addition to the peeled sticks that he placed in the troughs.
Ramban #1: After separating the sheep from the goats, he placed those with marked ankles at the head of the goats, and the Akudim and Chom at the head of the sheep. 3
Ramban #2: He separated all the lambs 4 mentioned in the previous Pasuk from the rest of Lavan's sheep, by forming them into separate flocks. Ohr ha'Chayim
See Ramban, who refutes this explanation.
According to Targum Yonasan, Yakov placed one such goat at the head of each flock (see Pirush Yonasan).
Ramban: According to other commentaries, Yakov placed only the Chom at the head of the sheep, since only such lambs were his (See R. Chavel's commentary).
And he explains "P'nei ha'Tzon" with reference to the aforementioned lambs (as if it had written 'Osam').
Why does the Pasuk mention brown sheep and sheep with marked ankles, and omit sheep that were spotted and blotched?
Seforno: Because it is speaking after Lavan had unilaterally changed the conditions. 1
Ohr ha'Chayim: This heats the animals more than seeing spotted and blotched.
Malbim: Lavan did not remove the Chom and Akudim among sheep, only among the male goats.
Why does the Torah sometimes call a lamb Kesev, and sometimes Keves?