I know Oro was feeling a missing of chakra but I still don't get why he would take his dna back from Kabuto. I would have took that moment as a prize. Why didn't Oro just kill Kabuto there and use him as an edo tensei summoning later? He was obviously op there and would have been a great addition to Orochimaru's arsenal.
The only problem I see with him doing this is that Kabuto probably knows the seal formula and can release it like Madara did. Even if he does know it, he still probably couldn't or wouldn't do anything about it. Madara had to wait until edo tensei was faltering to release it. Kabuto can't do that if he is completely binded. Even if he was to release it, im not sure if he would actually turn on Orochimaru. In essence, he would still be assisting his lord.
The only problem I see with him doing this is that Kabuto probably knows the seal formula and can release it like Madara did. Even if he does know it, he still probably couldn't or wouldn't do anything about it. Madara had to wait until edo tensei was faltering to release it. Kabuto can't do that if he is completely binded. Even if he was to release it, im not sure if he would actually turn on Orochimaru. In essence, he would still be assisting his lord.
so he became half man half snake 