What is Candling?
Candling is a way of
checking the fertility of an egg and the development of the embryo, with
the use of a light source in a darkened room. In a darkened room,
carefully hold the egg up to the light to observe the contents of the
egg.
Candling Results
The embryo is located at the large end of the egg, where blood vessels will be present under the surface if the egg is fertile. The embryo appears as a dark spot which becomes larger as the incubation period continues.
The embryo is located at the large end of the egg, where blood vessels will be present under the surface if the egg is fertile. The embryo appears as a dark spot which becomes larger as the incubation period continues.
Fertile egg
The egg will appear to have a black spot which as the embryo grows and incubation continues will grow larger until light will only pass through the air cell end of the egg.
The egg will appear to have a black spot which as the embryo grows and incubation continues will grow larger until light will only pass through the air cell end of the egg.
Infertile egg
Eggs appear clear.
Dead embryo
If the egg was fertile but the embryo has died then you will see a blood ring around the yolk or possibly a dark spot dried to the inside of the shell depending on when the embryo stopped growing.
Note that dark or brown shelled eggs are more difficult to candle than white or pale shelled eggs.
When To Candle
Candling can be done at any time, although day 8 onwards is usually when the embryo is more easily identified.
Day 3 of incubation (usually pale shelled eggs).
Day 5/6 of incubation (usually dark shelled eggs).
Between day 8 - 12 of incubation (embryo more easily identified).
3 days prior to hatching.
Day 5/6 of incubation (usually dark shelled eggs).
Between day 8 - 12 of incubation (embryo more easily identified).
3 days prior to hatching.
Out of the 14 eggs in this batch, we removed nine by day 14 that were obviously not developing. There is a chance that a non-developing egg will explode in the 'bator, and that is messy and STINKY. It hasn't happened to me yet, though.
I wouldn't candle after day 16 or 17. The eggs are mostly chick (black mass) and air sac by then anyway, and they should be left alone for the last few days before hatching (no turning from day 18-hatch).
Pics from day 8 candling
 |  |  |
| Store-bought non-fertile egg for comparison | Undefined, hard to tell if there's a chick developing | Spots like this may indicate bacterial contamination |
 |  |  |
| Nice air sac developing, a good sign | Nothing going on here! | This one had a faint ring, which is a sign of bacterial growth |
 |  |  |
| This looks undefined, but ended up hatching out fine | Well-formed baby inside! | Another good one |
 |  |  |
| good one | same one, slightly different angle | good one |
 | ||
| same one, slightly different angle |
