We should bear in mind that “cattle” = any domesticated animal, including sheep and goats. “Flocks” means flocks of sheep and flocks of goats, usually kept separate, Matthew 25:32. For the sake of simplicity, I shall call the two different sorts of animals “white” and “coloured”.
Verses 31,32 Jacob asks as wages from Laban all the coloured animals in Laban’s flocks.
Verse 33 Any animal found with Jacob that is white is to be reckoned as having been stolen by Jacob, and therefore given back to Laban.
Verse 34 Laban agrees to this arrangement, probably because he saw there were not many coloured animals in his flocks.
Verses 35,36 Just in case Jacob was trying to trick him, Laban removes the coloured animals himself, rather than allowing Jacob to do it as he suggested in verse 32. He puts his own sons in charge of these animals, and instructs them to keep the flocks at least three days journey away from the white animals that Jacob is now to look after. This will ensure they do not inter-breed and produce coloured animals, which Jacob would be able to claim. Jacob now has a flock of white animals that belong to Laban, and Laban’s sons are looking after Jacob’s coloured animals at a safe distance.
Verses 37-39 Jacob takes rods of three different trees, partly peels them, and places them in the water the flocks are going to drink. Now I do not believe that Jacob thinks that if you put striped sticks in front of breeding animals you get striped lambs. If that is the case, then how is it that some lambs were spotted? Nor do I believe it was simply a miracle, or else why was their need for rods at all? Certainly the birth of coloured lambs was of God, as 31:9, 12,13 indicate.
My suggestion is that by peeling the bark from these rods, Jacob released different chemicals, that had an effect on the genes of the males and females. Perhaps it was a combination of chemicals, if all three sorts of rods were placed in the watering troughs at the same time, or perhaps it was one chemical or combination of chemicals for the rams separately before they were put to the flock, and another for the ewes. So as they drank, the animals were taking in substances that would affect their offspring in the specific way Jacob wanted. It is a known fact that the colour of a child’s hair is the result of the contribution of both father and mother.
I have not been able to find any information which says this could happen, but advances in genetics are very rapid nowadays, so perhaps something will soon be discovered to show that Jacob’s strategy had a scientific basis. Those in the world who scoff at Jacob’s actions, and dismiss them as old wives’ tales, would be well advised to reserve their judgement.
When Jacob explained the situation to Rachel and Leah in 31:4-13, he tells them of a dream he had. He was not told what to do in this dream, but he saw that the rams that were with the ewes were coloured rams. Yet all Jacob’s animals were white at that point, even the rams. So perhaps in his dream Jacob is enabled to “see” the genetic makeup of the rams, so to speak, and God was telling him that those rams had the potential to produce coloured offspring, thus encouraging him to continue with his plan.
Verse 40 This is a difficult verse, but I suggest that it means that Jacob separated the coloured lambs that had just been born, (and we know from 31:8 that all the lambs newly-born were coloured), from the white ewes and rams that had produced them, and “set the faces of the flocks”, or, in other words, drove the flock of white rams and ewes towards the coloured flocks that Laban’s sons were in charge of, three days’ journey away. This achieves at least two things: 1. It shows Laban that Jacob is not set on cheating Laban, for he has now given him back the white animals he gave him. 2. It means that Jacob has the nucleus of a new flock, the males and females of which are all coloured, for he has sent the white rams and ewes back to Laban.
Verses 41, 42 Jacob now applies his scheme to the coloured lambs, and breeds only from them. But they are a mixture of good animals and not so good. So when the good animals were due to breed, the rods went into the water, and strong, coloured lambs were born. These were to be his, by the agreement. When the weaker animals were ready, the rods were not put in, and so weaker, white lambs were born, and these were to be Laban’s. Continuing this process, Jacob built up a flock of healthy, strong, and coloured sheep and goats. And he had done it for nothing, for Laban had given him the original white sheep, yet he had given them back to him, and only kept the coloured lambs. As a result, Jacob’s words came true that he spoke to Laban when they made their agreement- “So shall my righteousness answer for me in time to come, when it shall come for my hire before thy face”, 30:33. Laban had all his original sheep back, and more besides, for he also had the white ones that Jacob had bred.