When was the castration of young choir boys started by the Roman Catholic priests started and when was it prohibited?

In Europe, when women were not permitted to sing in church or cathedral choirs in the Roman Catholic Church, boys were castrated to prevent their voices breaking at puberty and to develop a special high voice. The first documents mentioning castrati are Italian church records from the 1550s. In the baroque and classical music eras these singers were highly appreciated by opera composers as well. Mozart's Exultate Jubilate, Allegri's Miserere and other famous pieces from this period now sung by sopranos and countertenors were written for castrati. Some of the alto parts of Handel's Messiah were first sung by a castrato. Famous castrati include Farinelli, Senesino, Carestini, and Caffarelli. The last castrato was Alessandro Moreschi (1858–1922) who served in the Sistine Chapel Choir. It was not until the late 19th century that the Roman Catholic Church officially condemned the production of castrati.

It was a cultural expectation at that time. Families wanted their boys to be chosen to be members of the choir. Castrato were treated well, having one in the family guaranteed status to the family and a better life.

It doesn't usually work to judge the past with today's standards and expectations. What was culturally acceptable in a different time may not make sense to us today, however, it was allowed and even desired at that time.

The last Castrato was around the 1930's in the Vienna Boys Choir. It sounds unbelievable, but they actually did this so they could sing higher notes.

Wrong side of the Church it was within the Byzantine Empire in which around 400 AD in which Empress Aelia Eudoxia had her eunuchs sing as choir boys in the Church. This custom lasted until the Western forces sacked Constantinople during the Fourth Crusade in 1204 AD, the Western Church ended that tradition. Of course the practice of castration was brought over to Spain by Muslims when Spain was under Muslim rule during the Middle Ages in which eunuchs served as harem guards.

The castrato parts in operas such as Handel's Julius Caesar are sung by counter-tenors these days.

It certainly did happen. After it was made illegal some choir boys still had unfortunate "accidents" in which they lost their testicles, to provide the castrati voice. I believe there is a very old recording of one of the last castrati (heard it on BBC years ago).

http://en.m.wikipedia.org/wiki/Castrato

It never happened. Choir boys have parents, do you really believe that they would allow them to be mutilated ?