Think you are hearing Culled or Cull. It does not necessarily mean killed. In cases where you are talking about sick or chicks with health problems it probably does mean it was euthanized. In cases where the bird is healthy but you don't want to use it for breeding for some reason (like in the cases of what should be an autosexing breed, you don't want to breed from birds which are not obvious at hatch) it can mean just to remove from the breeding program. ie you can cull birds from your breeding flock and put them into your laying flock or sell them etc... in that case it is used to just mean remove or eliminate from something.
cull
[kuhl] Show IPA
verb (used with object)
1.
to choose; select; pick.
2.
to gather the choice things or parts from.
3.
to collect; gather; pluck.
noun
4.
act of culling.
5.
something culled, especially something picked out and put aside as inferior.
