In the Christian world, bestiality has always been frowned upon. Sexual activity is seen as being for the purpose of creating more Christian babies. It is openly referenced in the penitentials (http://www.anglo-saxon.net/penance/animals.html)of the early middle ages, these books attempted to create tariffs for working off sins and covered issues of morality and sexual purity. These penitentials often provided contradictory tariffs, even contradicting themselves about how long it would take to work off these sins.