Candling Eggs

Candling Eggs is an easy process that gives you assurance that your eggs are fertile and developing correctly after a short period of time in the incubator. It allows you to remove infertile eggs and soon you will start to be able to identify ‘bad eggs’ and remove these as well. The candling photos on this page should help you to identify these.

candling-eggs

Candling an egg in the dark using a special candling torch

Although it has never happened to me, bad eggs can sometimes explode or ooze in the incubator causing bacteria to contaminate the other good eggs, causing them, in turn to go bad.

I usually candle my eggs after a week of incubation. It can of course be done before this but the first week of incubation is the most critical in terms of getting the correct development of the embryo so leaving the eggs alone during this time is good practice. After a week, we are a third of the way through incubation and it is far easier to identify fertile eggs, even if eggs have a dark shell as is the case with Marans.

How to candle eggs

You will need a bright light and a way of shining this through the egg. Candlers can be bought online from poultry shops, or you can make one using a bright light and a cardboard box with a hole cut out for the egg to sit on. Try to get the best seal around the hole and candle in a dark room to see the best results.

Candling Dark Eggs

If the shells are dark or have pigments / marks on them, it can be difficult seeing the embryo. I rock the egg from side to side very gently so the contents move. This must be gentle, or you risk damaging the Chalazae that hold the yolk / developing embryo.

“The Chalazae is the structure that suspends the yolk within the egg. It can be damaged by shocks and vibration”

Remember not to candle for too long if it is heating the egg. I spend around 8 seconds per egg before trying the next one.

What to look for after a week

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Candling an Egg at Day 7, the embryo is clearly seen in the dark.

After 7 days, you should be able to see development of the embryo, including spider like veins and even (if you are lucky) a little movement. The embryo often sits on one side of the egg so be sure to rotate the egg around slowly to get the best view. Occasionally, you may see a tiny heart beating if it is close to the edge of the shell.

Look for fertile and non fertile eggs. Clears as they are called are easy to remove after 7 days. If you have a number of eggs in the incubator, it soon becomes clear which eggs have developed correctly.

By day 7, you should clearly see the embryo. Don’t forget to turn the lights out in the room when you do this so you get a clearer picture!

What to look for after two weeks

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By day 14, the embryo is taking up around two thirds of the egg shell,

After 14 days, the embryo is well developed and turning into a chick. Two thirds of the egg is now covered and it is hard to see any detail.

Look for embryos that have developed so far but died. This can be for a number of reasons, including incubation technique, damage to the chalazae (which can happen when eggs are dropped / damaged in the postal system for example) or become infected with bacteria. A red ring is sometimes seen inside the egg which is the bacterial infection.

The photo to the right shows how much of the egg is now filled with the embryo / soon to be chick. It is more common to see movement inside the shell.

Bad Eggs

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A bad egg at day 14. The embryo has died.

If an egg appears bad, it can be removed to prevent it from exploding and contaminating other eggs. Bad eggs can look different every time but if you compare them to the bulk of the other good eggs in the incubator, it won’t be long before you can recognise a bad egg from the rest. The bad egg shown to the right was found at day 14, two weeks into incubation. Clearly comparing this to our last photo, there is a problem.

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The contents of the bad egg.

Bad eggs don’t change – so if you are unsure, mark it and have another look a few days later to see if it still looks the same.

The second photo shows to the right shows the contents of this bad egg after it was opened on a plate. I wouldn’t normally do this because it can be smelly but was worth while to show what the contents looked like, clearly not a nearly developed chick!

There are a few more photos on poultrykeeper’s candling chicken eggs page here.

129 Comments

  1. Hi, Me and my roommate have ‘saved’ two chicken eggs from a practical in our study. The eggs that weren’t used in the practical would have been thrown away, so we brought two eggs home. The eggs were 6 days old when we got them and it’s been 11 days now since the practical, which would mean the embryo’s are 17 days old now. I’ve kept the eggs under a warm lamp (not any fancy incubation-gear, since we’re poor students) and turned them over a few times a day. When I candled them today (for the first time, I only found out about candling today), both have a clear spot of about 1/4th of the egg and I can see some veins in the yolk right above the clear spot, but the rest of the egg just seems like a black mass. There is no clear movement or anything… I wonder if they are still alive. Would you have any idea?
    Thanks in advance.

  2. I am a beginner at egg hatching so I do not always know what to look for. I do understand that, when candling, a dark spot can indicate an early death but all the remaining eggs look totally different inside. Some have a shadow to one side, some towards the top and some are completely dark except for the air pocket which I can see clearly. Is this normal? Are the chicks alive?

    • They sound normal. A dark patch is usually the yolk. Within this you can often see veins after a week and a dot (the embryo). A really black spot after 2 weeks or more is where this embryo started to develop and then died. The other eggs will show an enlarged embryo about the size of the yolk after this time so it will be obvious which eggs have developped and which were fertile but then died an early death.

  3. I have been told by a poultry farmer that when incubating eggs in this country, because we are an island surrounded by water, we do not need to add water to the incubator as too much humidity could cause the chick to become stuck to the shell. Is this true?

    • An incubator with automatic humidity control regulates the humidity inside the incubator. A manual incubator is regulated by you. If the humidity is too high inside then reduce the surface area of water inside… until there is no water and then it is as low as you can get it without having drier air outside the incubator. Being close to a river or stream, or having wet weather or being on an island surrounded by water all affects the humidity of the air. The only real way to see is to measure it and make adjustments until you get it as close as you can. Candle your eggs regularly to check for the size of the airsac too. There are charts in most books on incubation to show the air sac size and therefore correct moisture loss from the egg with time.

  4. I have had my eggs in incubation for 22 days now… I candled today because I didnt see or hear anything like hatching… I really dont see much. When I candled at 18 days, I saw what I thought to be movement and veins in at least one… The rest were very dark throughout… Now, they all just seem dark throughout… Any thoughts? Did they not survive?

    • At this stage, they should be dark, and you won’t be able to see through. Only the air sack will be visible.

  5. Your page has been a great help to us newbees.I had asked a question earlier which you had not replied to but im learning as I go.The eggs that I placed as aforementioned are hatching now.Do all chicken eggs not take 21 days to hatch? These are hatching around 16-18 days.Four chicks have hatched so far and are doing well but today there was one that appeared unable to fully break out as it seamed the membrane had dried out.I read up on how to help him out a bit and within 30 minutes he was out hopping around.I have another that piped this morning and has been rocking the shell most of the day but the past few hours it has stopped with no progression of the shell opening.Could this bird have passed?I raised the humidity level to mid to higher 70%.From past research this should be correct?I had maintained 60’s prior to hatch but once they started to hatch I raised it.Are my procedures correct and my % correct at hatching?How does the humidity percentages affect the hatch?

    have one that piped this morning and have been watching it closely all day.It was physically moving the

    • Yes, they take 21 days. If the temperature of the incubator is too high, they will hatch early but you risk other problems then. You shouldn’t really help them out or you may find it is too soon and then they bleed to death. They need to absorb the yolk sack after pipping to give them the strength to break out. Weaklings should really be left, or in future generations you are introducing weaker chicks.

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