It's a trait that was bred into animals for years and years before we humans started stringing up wire all over the place and genetically manipulating them.

Bull elk, and other animals, still do this in the wild in an attempt to keep satellite bulls from stealing cows from their harem during breeding season.  The dominate bull will defend his group from young bulls allowing nature's survival of the fittest to continue to exist via his earning the right to breed as much of his group as he can.

When we move cows, we humans have become the new "satellite bull" and are attempting to move "his cows" without his approval.