Candle eggs with egg candling lamp to gauge the extent of embryo development.

1. Clear when candled - probably infertile (or very early death) when candled at 8 days.
2. Fertile with red blood vessels - after 8 days.
3. Red or black staining - early death when candled at 8 days.
4. Embryo with red blood 'ring' - early death when candled at 8 days.
5. Dark outline with ill defined detail - late death (10-16 days).
6. Live embryo with bill in air sack - due to hatch in 24-48 hours.
7. Normal development of the air pocket according to number of days.