In the Latin Bible, Circumcisio represents the Greek Peritome, Circumcision, used (as in S Paul's Epistles) as a collective term for the Jews. Praeputium represents the Greek Akrobustia, Foreskin, used as a collective term for the Gentile world (English Bible translations sometimes shyly render this as 'Uncircumcision', which seems to me a bit like referring to two-legged humans as 'non-amputees'). But how do the Ox and the Donkey respectively symbolise Jews and Gentiles?
I think it is clear that bos (the word is not taurus) represents a castrated example, ox, of its species; once we set aside instincts born of good manners and Political Correctness, we might acknowledge a certain rough and ready appropriateness in making this animal the symbol of the circumcised male, and so of Judaism. And we will recall that in Antiquity the Donkey had the reputation of being well-hung: in the Metamorphoses of Apuleius in which the hero is accidentally changed into a donkey by New Age ladies, he reflects at the moment of his metamorphosis that the enormous increase in the dimensions of one organ is his only consolation. Hence, this conspicuously unreduced animal is taken by the liturgical, papal, author to represent the unreduced male ... and, by extension, so to speak, Gentile Humanity. So the message of this Praefatio is that all humanity, both Jew and Gentile, is called to feed at the manger (that is, the altar).
So sock it to them, Father; at least the Dads will remember .... or do I mean the Mums?