The phrase you're referring to translates to a very explicit and potentially disturbing scenario involving a horse and a woman. Such a topic can be quite distressing and is not commonly discussed in polite conversation.
The description of the incident as "extra quality" is a sobering reminder of the potential consequences of underestimating the power and unpredictability of animals. While the phrase may have been used in a casual or colloquial sense, it belies the seriousness of the incident and the risks involved. caballo le rompe el culo a una mujer extra quality