There's an old Japanese idiom that says, "A duck comes along carrying a leek". It means a happy convenience, as duck with leek is a popular meal. The Pokemon Farfetch'd is based on this saying. The anime also states they are rare due to them being delicious. It seems that Farfetch'd were designed to be eaten from the very beginning. Any notion of them being used as food was later toned down or dropped. Along with the word "leek", which is now called a stick or a stalk.