What Child is This?

The great Christmas hymn "What Child is This?" states on the first line of the second verse:

Why lies he in such mean estate, where ox and ass are feeding?

This prompted a discussion with Tirzah that went like this:

Tirzah: "What are ashes?"
Daddy: "An ass is a donkey."
Tirzah: "No it isn't."
Daddy: "Yes it is, it's another name for donkey."
Tirzah: "Donkey's don't like being called asses, because they are used to being called donkey's."
Daddy: "Donkey's don't mind being called asses, they have been called asses for a long time."
Mommy: "Ass is used in songs instead of the word donkey."
Tirzah: "I don't like asses."