We do everything possible to reduce the incidence of late hatch chicks. Even with meticulous protocol for setting older eggs and slower hatching breeds at the proper times to achieve a narrow hatch window late hatchers always occur.
To increase the quality of late hatch chicks we combine all wet chicks in common baskets so they stay warmer and benefit from the close contact with one another. This is done after the hatch has been completed and only these late chicks remain for up to12 hrs. In our case .2-.5% on a good hatch seems to be the norm. This % increases with older eggs and poor weather conditions.
This practice reduces the # of chicks with weak legs but has no benefit for the truly deformed chicks.
It is our practice to euthanize non-viable chicks by cervical separation when we are doing the hatch. These chicks are then frozen and donated to a wildlife rehabilitation organization.
The hatch debris that may contain live unhatched chicks is bagged and CO2 is pumped into the bag euthanize them before disposal.