Virtual Nativity - The Ox and the Ass

The ox and ass are included in Nativity art from the very beginning, even when Mary and Joseph are absent. This 4th century sarcophagus lid, preserved beneath the pulpit of Sant'Ambrogio basilica in Milan, shows the two animals flanking the Christ Child in the manger, without Mary or any other human attendants.

The Biblical narratives of the birth of Christ do not mention the ox and ass.  The only animals mentioned in the Gospels are the flock over which the shepherds watched:  

“In that region there were shepherds living in the fields, keeping watch over their flock by night.”
Luke 2.8

Yet, besides the Christ Child himself, the ass and the ox are the most ancient and stable elements in the iconography of the nativity.

Possibly the Fathers of the Church saw in these words a prophecy that pointed to Christ's birth and particularly to the fact that Christ was laid in a manger used as his crib. The Fathers reasonably surmised that there would be animals around the makeshift crib, notably the ox and donkey prophesied by Isaiah:

“The ox knows its owner, and the donkey its master’s crib; but Israel does not know, my people do not understand.”
Isaiah 1.3