The best time to candle eggs is after they have been in the incubator for 7 to 9 days. The embryo is very fragile during the first week so you should wait till after this critical period has passed. You will be able to see what is going on more clearly as well after 7 days or so.
Below: What you should see in a fertile egg after 7 to 8 days in the incubator.
What is candling eggs?
Candling eggs for fertility is simply means shining a bright light into the egg. It is how you see if an unhatched egg is alive without breaking the shell.
Chicken farmers use candling to learn which of their chicken's eggs are fertile and will hatch into baby chicks. Candling can also be used to tell if a fertilized egg has stopped developing. The candling process works by illuminating the interior of an egg so you are able to see what is inside the shell, and the level of development of the unhatched chick prior hatching.
Below: An egg being candled.
Candling is the act of simply shining a light through an egg. White and light coloured shells are the easiest to candle, while darker shells will require a brighter light.
The simplest way to candle an egg is with a basic flash light, but there are specialized pieces of equipment designed specifically for the job (candler/ candling torch). It is mostly done on the 7th day of incubation.Do not keep the egg out of the incubator for more than 5-10 minutes, and don’t candle the eggs all at once. To allow the eggs to stay inside the incubator, plan to candle a few at a time.
In brief if the eggs you are looking at are:
- Clear. If the inside of the egg is clear and free from visible structures or dark areas the the egg is infertile or the embryo died very early. Remove this egg from the incubator.
- Blood ring. If a ring of red is visible within the egg, there was an embryo at some point, but it has died. Remove this egg from the incubator.
- Single dark spot. These have dies around the 8 day mark and should be removed.
- If you can see a spiders web of blood vessels within the egg, there is a live embryo inside. Blood vessels in chicken eggs are normally observable from 3 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.
After 21 days you can candle the eggs that fail to hatch to see if the embryo is alive or not before discarding the eggs. You can also be able to diagnose the reason for not hatching.
When is the best time to candle eggs to check they are fertile?
The best time to candle an egg to see if it is fertile is 7 days . From 5 days to 10 days into incubation will be fine. Go for 10 days if you want to be extra cautious.
Below: If you are lucky you should see something like this moving around inside the shell.
You can see the spiderlike veins of the embryo before this time but leaving it for a full week will allow those that are going to die early to do so. These are the blood ring eggs.
How many times should you candle eggs during incubation?
You should candle three times during incubation:
- Before you set your eggs in the incubator to make sure they are viable and not damaged.
- Once at 5 to 8 days to check fertility and remove clears.
- Again at 16 days before hatching. Remove any dead or undeveloped eggs or newly hatched chicks may get covered in smelly goo for explosive eggs.
Candling eggs before incubation can help show up any abnormalities in the egg that would prevent it from hatching. You would be able to see if the egg was missing it's yolk, cracked, had a damaged air sac or had a problem with the shell.
Embryos often start developing at then stop. Candling around the 7 day mark will allow you to remove clears and early dead eggs.
Candling the day before pipping is due to start will mean you can remove any late quitters.
Does candling hurt eggs?
No, not as a rule but it can do if you take too long or are not careful. If you leave an egg on a hot lamp for too long it may damage it and if you leave an egg out of the incubator to go cold for too long it may die. This is only really a problem is you have a large number of eggs to candle at one time.
The more you candle egg the greater the likelihood you will crack or damage one as well so take great care and used soft towels under your work area.
How early can you candle eggs?
With a white shelled egg and a powerful enough light you can see the development of the embryo just 24 hours after incubation has started.
It is difficult at this stage and not every egg that starts will finish. Also the embryo is very susceptible to damage during these early days with the membranes and newly formed vessels being easily damaged if the eggs are knocked
Is there anyway to candle very very dark eggs?
I measure the size of the air sack on my Marans eggs, and incubate one or two light eggs with them to compare air sack size to.
Can you candle eggs with a smartphone torch?
Yes you can and it works very well. They light is bright and just the right size.
Below: An eggs being candled with a smartphone torch.
To candle an egg with a smartphone torch, turn the light on and put the phone face down on a flat surface. Hold the egg over the lamp. This actually works better if you have a cover on the phone as you get a little groove to rest the egg in.
When is it too late to candle an egg?
It is only too late to candle after the rest of the eggs have started to pip. Opening the incubator after pipping will effect the humidity and might shrink wrap the chicks killing them in their shells.
Can you candle eggs too often?
Yes, opening the incubator too often messes with temperature and humidity and the more you handle and move the eggs the greater the risk of dropping or cracking the eggs or adding bacteria by contamination from your hands.
Should you candle eggs before incubation?
Yes you should candle your eggs in preparation for incubation. You are looking for cracks, No yolks or double yolkers and damaged air sacs
Should you candle eggs under a broody hen?
If there’s a mom involved. I don’t see a need. I rarely candle eggs under a broody hen as it can be very disruptive. The best thing to do with a hen on eggs is wait till she gets off to feed and then inspect the eggs visually.