It is important to note the role that meat takes in subsistence agriculture: Chicken, for instance not only produce eggs and manure, they also serve as breathing refrigerators: Whenever there is the need, especially in the winter, one can easily kill one or more and eat them. I think cattle plays a similar role at a larger scale.

Obviously, we have moved very far from these basics and industrialized the whole chain, but it should be worth considering that mass adoption of vegan food requires the very same industrialization whereas true organic food will profit from a certain amount of livestock.