Purpose of Second Candling (Day 18) in Incubation

Correct Answer: Dead-in-shell

The second candling on the 18th day of incubation is done to discard dead-in-shell eggs before the eggs are transferred from the setter tray to the hatcher tray. At this stage, dead-in-shell eggs appear as a dark, opaque mass with no embryo movement.

Dead-in-Shell Condition

• Cause: Poor ventilation (low O₂ / high CO₂) and/or faulty turning of eggs.
• Appearance at candling: Completely dark/opaque without any movement or blood vessel pulsation.
• Why remove before hatcher? If left in the hatcher, dead-in-shell eggs can burst or rot and contaminate live, healthy eggs.

Comparison of Two Candlings

Why Other Options Are Wrong

• Piped eggs → these are hatching eggs found on day 21; not discarded during incubation.
• Infertile eggs → already removed at 1st candling on day 7.