Yakov’s possessions were mainly sheep. He traded in some for bulls and donkeys, because at his core he was submissive as a sheep. His ego was completely submitted to the ultimate truth and power, Hashem, and therefore if he had an adversary and needed to fight them, he would stand up forcefully and strongly like a bull and a donkey to fight his enemy however he knew he wasn’t fighting from his ego, but from his complete submissiveness to the ultimate power, Hashem.

לקו״ש טו- ג