Why do cows (and other hooved animals) need a hierarchy?
Could not fit in a comment...

There are several issues with your question. 


The correct question is not why such species need something but rather why it occurs in this species. In other words, why did a hierarchy evolved in a given species?
It is unclear to me why your are interest in cows (or other grazing animals) rather than any other species that has some kind of hierarchy and therefore your question is a bit unclear.
There are several questions in your post. A post should always be limited to one question.
I personally have never heard of the concept of "advertised fitness". How do you define it?
I am not sure how much you are interested in the evolution of social traits and especially about reputation and how much you are interested in Machiavellian intelligence. In any case, you may probably want to read about the evolution of social traits (kin selection, it may take you some time) and about the social selection pressures for the evolution of cognition, such as Machiavelian intelligence.


For all those reasons I vote to close. But I hoped that those comments can help you to clarify your post and to seek for more information.