A billy goat is a male, not castrated goat.
Billy goat may also refer to:
Billy Goat (band), American band William Windsor (goat), a goat also known as Billy the Goat Billy Goat, a character in the Donald Duck universe The Billy Goat Tavern, a chain of taverns mostly in the Chicago area. Sergeant Bill, a Canadian WW1 military mascot
See also Curse of the Billy Goat, a sports-related curse supposedly placed on the Chicago Cubs Major League Baseball franchise