Don´t know if the bull are supposted to do what it does or if they just haven´t think about it.
Today when you move the bull and that runs away, it destroy the crops they run throug. If it supposted to do that I then guess the bull does what it should. But otherwise my suggestion are that the bull should collect the crops when they run throug them. Then it will do little like the tractor booster and will be more useful.
As it it now sometimes you have to avoid moves around the bull because they destroy the crops you need.