Purpose of First Candling (Day 7) in Incubation

Correct Answer: Infertile eggs

The first candling on the 7th day of incubation is done to identify and discard infertile eggs. By day 7, fertile eggs show clear blood vessel development, while infertile eggs appear clear (transparent) with no development.

Why Infertile Eggs Must Be Removed Early

• Infertile eggs do not hatch and occupy valuable incubator space.
• Over time, infertile eggs can become contaminated, develop bacteria, and explode inside the incubator, contaminating other eggs.

Appearance at 1st Candling (Day 7)

• Fertile egg: Dark embryo (black spot) visible surrounded by a network of blood vessels like a spider-web.
• Infertile egg: Completely clear, with only the yolk shadow visible — no blood vessels.
• Early embryonic death (blood ring): A ring of blood visible but no further development — these are also removed.

Why Other Options Are Wrong

• Dead-in-shell → identified at 2nd candling (18th day).
• Piped eggs → these are eggs where the chick has started breaking the shell (day 21); not seen during candling.