This usually happens several days before birthing. Bulls have to determine which one of them is dominant. A fight between bulls that weigh about the same may last more than an hour and will not end until one hollers calf rope. Bulls get very possessive of their herd of cows and will walk the fence chasing any and all cows and calves away from it if other bulls are within cruising distance of the fence. If you hear an extreme blast of air from the bulls nose you and the cows will move away from the fence or else pay for the bruises.
Bulls get the best feed by pushing everyone else out of the way.
Bulls don't mind if younger bulls follow them around and watch during training sessions. Just like elephants, they know when you are removing a loved one and won't take kindly to it. Your emotions may get involved too, when you hear the dramatic trumpeting of the death march to the burial ground. Keep the family dog away from the cows unless it is a cow dog there to work cows. Cows don't need to like your dog any more than they should like coyotes.