[Detrytus]

The common practice is that you butcher bulls at young age, but you keep cows for milk - you actually make much more money on milk than on meat.

With chickens it's even worse: males are killed immediately after hatching, because their meat is worth next to nothing. Females are kept for both eggs and meat.

[kevinmchugh]

My understanding is that chickens are bred either for eggs or for meat. Egg farmers cull males as soon as they can (which depends on an interesting technical problem called sexing). Hens that can't lay anymore are called "spent hens", and the meat is not generally liked by Americans at least, so it's probably not what you're buying at the grocery store.

Poultry farmers raise both sexes and slaughter as soon as the bird is large enough.