Animals eat other animals
We should not base our ethics as a society on what animals do in nature. Lions eat their offsprings if they don’t have enough food, engage in violent territorial disputes and forcibly impregnate females. Dogs smell each others’ backside when they first meet. Many animals even kill members of their own species. If we say that animal behaviour is a basis for human morality, we could advocate murder, infanticide, rape and several other unethical and/or disgusting behaviour that are commonplace in nature.
Another crucial point is that animals in the wild kill to survive. We don’t need to eat other animals to survive, and doing so causes suffering, so if we can avoid it, we should. Animals are clearly not good ethical role models.