How to Candle Chicken Eggs

Inside: Learn how to candle chicken eggs: a step-by-step guide to determine fertility and monitor development. Essential tips for a successful hatch.

When we first started the process of hatching our own eggs I thought the idea of candling seemed really simple, how hard could it really be? But it turns out how to candle chicken eggs can be a little more tricky than you might think.

candling of chicken egg with How to Candle Chicken Eggs  text overlay

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How to Candle Chicken Eggs

During the process of incubating eggs, there are a few different times that you want to candle your eggs to see what their development is. Why? Because you aren't going to continue to incubate eggs that are not developing.

Eggs do have the potential to explode if they are left in the incubator if they are not developing but still being held at a high temperature.

What to Use to Candle Eggs

What you use is going to depend on the size of your egg, and what you have for candling. My small incubator does have a built-in candle which works great and is what I use the most of the time.

You want to have something that the eggs fit on nicely, or that you can also wrap your hand around the make it tight-fitting. You can see a demonstration of this below in the photo where I was candling to test fertilization.

Candling an egg for fertilization

How to Candle Chicken Eggs

What you want to do is sit the egg on your light source as in the picture above. You want the light to not be shining out around but just through the egg.

Gently touch the light source to the pointed end of the egg or hold it a short distance away to create an illuminated glow inside the egg.

Remember to take care when candling and to move quickly so that your eggs aren't getting too cold, but not so quickly that you drop an egg. A friend and I both have dropped eggs and killed potential chicks.

I remove hatching eggs one at a time to candle and then back into the incubator. Yes, it can be a slow process but I don't want to cause problems with heat loss, or humidity changes.

candling eggs - different stages of incubation

What You Are Looking For

Look for visible signs of development. In the early stages, you may see veins or a network of blood vessels. As the embryo develops, you might observe a dark area with a moving shadow (the developing chick) and air cell growth.

Day 1-7:

  • Cell division and formation of the embryo.
  • Blood vessels start to develop.

Day 8-12:

  • Organ development begins.
  • The embryo takes the shape of a chick.
  • Blood vessels become more visible.

Day 13-17:

  • Feathers start to develop.
  • Beak, claws, and comb become visible.
  • Movement inside the egg becomes more apparent during candling.

Day 18-19:

  • The embryo fills most of the egg.
  • The yolk sac starts to retract into the chick's body.
  • Chicks begin to position themselves for hatching.

Day 20-21:

  • The chick is fully developed.
  • The chick internally pips the air cell (takes its first breath).
  • An external pip (hole) appears on the eggshell.
  • The hatching process begins.
Poultry Incubation Course image
Poultry Incubation Course.

Why Candle Eggs

You want to candle eggs periodically to make sure they are developing so you can remove them from your incubator if they are not.

You will want to candle your eggs on days 7, and 15, and the final time would be day 18 before you lock down your incubator.

Not every egg is meant to be a chick, not all eggs get fertilized even from one hen. Hens can reject sperm from the rooster.

There can also be contamination that happens which will prevent an egg from developing.

You definitely want to remove eggs that have been contaminated.

Remember to take care when candling and to move quickly so that your eggs aren't getting too cold. You don't want to candle them too often because this is going to increase the time they are out of the incubator away from that heat and humidity.

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    Frequently Asked Questions

    What does it mean when an egg is dark when candling? 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.

    What does an unfertilized egg look like when candled? During candling eggs with a developed embryo will appear dark. A clear egg may be infertile or contain an early dead embryo.

    Choosing the Right Egg Incubator

    Getting Started with Incubating Eggs

    How to Tell if Eggs are Fertilized

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