Why did Yakov send the animals in groups with breaks in between?
Rashi: He did this to maximize the effect of the gift, to surprise Esav with its magnitude 1 and satisfy his greed.
Seforno: So that Esav should take note of the fact that he had sent him couples in a way that was most beneficial to him (as the Pasuk explained earlier), 2 inasmuch as it would increase rapidly. 3 Moreover, he instructed them to leave a space between the groups 4 , to avoid the animals jumping from one group to the other, thereby losing the desired effect.
Rashbam: He sent the gift in a way that is more dignified.
Hadar Zekeinim says that there was Mil (about a kilometer) in between. Rashi says that there was a day's journey (40 Mil) or less in between.
As Yakov specifically intimated, when (below, 33:11), he refers to the gift as 'a blessing' (Seforno).
Ha'Emek Davar: Also initially, each species was by itself, lest improper slaves mate animals with a different species.