"Cow and calf" comes about from arguments about book copying. The life of St Columba provides a source for sixth-century monks arguing about copyright. Columba copied a psalter, and wanted to take it away. Finnian argued the copy belonged to him, the book's owner. This argument spilled over into warfare, and the king got involved and declared "To every cow belongs its calf; to every book its copy."
See: here and here for versions of the story.
(As an aside, there's no argument that a calf belongs to the cow - if you want to borrow or rent a cow for milking purposes, the cow only produces milk if it's had a calf, so you have to keep breeding your milk cows. However, if everyone you rented or loaned a milk-cow to kept any female calves born, they would soon have enough cows they wouldn't need yours. Therefore it was commonly agreed that if you borrow someone's female animals, any babies they have belong to the original owner unless you've already made a deal to purchase any offspring)