Cow or sheep?! The chorus mentions a cow (bó) and a sheep (caora). The verses are about a sheep. There are two main theories:
Theory 1): at some point two or more songs were combined. Probably "A dhroimeann donn dílis/O (my) white-backed brown darling (cow)", "An tsean-chaor' adharcach/The old horned sheep", "Bó leath adharcach uí Mháirtín/Martin's one-horned cow", "Ewe with the crooked horn", etc.
Theory 2): This song (apart from "A dhroimeann donn dílis") is actually about a Poitín still and the money the owner makes from it, the horn being the worm (the copper piping where the Poitín mixture condenses. It is usually or often a spiral, so maybe curved like a ram's horn).
If so, since the Poitín still with its "one long horn" was illegal in Ireland, it couldn't be sung about openly. It fed him well and put a "jacketeen" on his back.