What is Candling?
If you have chosen to candle the eggs, then the optimal time to do it to test fertility is between days 7 and 10. Ideally use a specialised candling light, and always candle in a darkened room to have the best chance of seeing inside the shell.
To successfully hatch out chicks you do not need to candle eggs. Especially if you are new to hatching, then you may want to wait until you have a few hatchings under your belt before you take on this new skill!
However when done correctly, candling can help sort the fertile from the non-fertile eggs, and it manages your expectations regarding the number of chicks you can hope to expect.
How to Candle an egg
You will likely see three different options.
- If the inside of the egg is clear, that is, you cannot see any visible structures or dark areas, then this egg is not fertile. You can remove this egg from the incubator.
- If you see a ring of red within the egg shell, this means that at one stage there was an embryo, but it has since failed to develop. You can also remove this egg from continued incubation.
- If you can see blood vessels within the egg, there is a live embryo inside. Blood vessels in chicken eggs are normally observable within 7 to 10 days of an egg's incubation. By 18 days of incubation, the embryo takes up most of the egg and appears as a dark area within the egg. You can sometimes see movement inside the egg.
If you notice broken or leaking eggs, remove them from the incubator as they are not likely to be viable and may contaminate the incubator. After candling, return eggs to the incubator and return to the day 1-18 turning schedule.
With candling it is important to be careful and quick. An incubated egg cannot be away from its optimal temperature and humidity for more than a few minutes. If it is, then you could potentially turn a fertile and viable egg into one that stops developing from that point.
If you have a large number of eggs to candle, it may be better to do a few eggs at a time.