Understanding Egg Candling: A Detailed Look at Chicken Embryo Development

Every backyard chicken hobbyist knows the importance of monitoring the health and growth of their flock, but what about before they hatch? This is where egg candling plays a vital role. By peeking inside your eggs before you spend a lot of time incubating them, you can avoid wasting your time waiting on, well, nothing to hatch.

What is Egg Candling?

Egg candling is a simple, non-invasive technique that uses a bright light source to illuminate the contents of an egg. Originally, this was done with candles (hence the name), but today, specialized LED tools are often used for this purpose. 

My parents owned a general merchandise store in the 1960s. I remember them taking cases of eggs into the darkest room in the building (a windowless bathroom) and getting down on their knees to candle egg after egg after egg. They had to do it so they didn’t sell fertile eggs for consumption to their customers. 

Why is Egg Candling Important?

Egg candling is the secret tool of every successful chicken raiser. It’s the window into the fascinating world of the developing chick. This method helps you identify fertilized eggs, track the embryo’s progress, and spot any problems early on, helping you avoid cracked eggs and identify and discard the unfertilized ones.

Cracked eggs might allow bacteria inside the egg, killing the embryo and possibly contaminating your incubator.

Tools Needed for Egg Candling

For a detailed egg examination, a good quality candling light is essential. Look for one with high lumens and a small aperture for best results. Here’s a top pick of mine: Magicfly Rechargeable Wireless Egg Candler Tester for Monitoring Eggs Development, Bright Cool LED Light Candling Lamp.

How to Candle an Egg

Candling an egg is simple, but it requires a gentle touch and attention to detail:

  1. Prepare your workspace: You’ll need a dark room and a flat surface.
  2. Hold the egg: Place the egg’s larger end on the light source.
  3. What to look for: Look for signs of veins, a dark spot (the developing chick), or clear indications of yolk for infertile eggs.

Remember, be gentle to prevent damaging the delicate life inside. In fact, I wouldn’t candle an egg for the first week of incubation because this is the time when embryos are most fragile. After 7 days and up to day 15 is when candling is best done.

 After 15 days it is best to let the chick come peacefully into the world without a lot of disturbance. This practice will help to increase success and decrease chick mortality.

Stages of Chicken Embryo Development through Egg Candling

Using egg candling, you can witness the miracle of life unfolding day by day:

Day 1-3

At this stage, you’ll see little more than the yolk, but if you look closely, you might spot a small cluster of cells.

Day 4-7

You’ll begin to see spider-like veins appearing – this is the circulatory system developing.

Day 8-14

The embryo grows, and the egg’s interior becomes darker. The movement might be visible.

Day 15-Hatching

The chick fills most of the egg at this point, and movement becomes more apparent.

Interpreting Candling Results

Interpreting candling results is part science, part art. A dark interior with clear veins usually means a developing chick. If you see only a clear yolk, the egg is likely infertile. If there’s a dark mass with no movement, it could be a dead embryo.

Common Problems Detected through Egg Candling

Egg candling can help you spot potential issues early. For example, cracks, blood rings, clear eggs, or dark, unmoving masses could indicate a problem. If you detect an issue, the problem could be infertile eggs to start with, too much handling, unstable conditions in the incubator, or stable conditions but wrong settings in the incubator. Consulting a chicken-raising expert might help.

Frequently Asked Questions about Egg Candling

Egg candling is one of those topics that you don’t hear much about. Let’s face it: not many people who buy home incubators candle. But as hobby farms gain interest and backyard flocks increase in popularity, candling is becoming a fascinating and vital part of raising chickens, providing valuable insights into the development of the chick within the egg. 

As backyard chicken raisers become more sophisticated in their practices, many questions about egg candling arise. Let’s address some of the most common ones.

What is the purpose of candling eggs?

Candling eggs serve several important purposes in poultry farming. Firstly, it allows chicken raisers to check if an egg is fertilized and developing properly. This is critical in avoiding wasted time incubating infertile eggs. Secondly, egg candling enables the detection of any problems at an early stage, such as dead embryos, which can risk the health of other eggs if not removed promptly.

Is candling an egg a test of fertility?

Yes, candling is a primary method used to test an egg’s fertility. By shining a bright light into the egg, one can observe certain signs of fertility, such as the development of veins and the embryo. However, it’s important to note that signs of fertility are not immediately apparent and usually become visible several days into the incubation process.

Are store-bought eggs candled?

Yes, most commercially sold eggs are indeed candled as part of the quality control process. This is primarily done to check the egg’s interior for any physical defects, blood spots, or signs of disease. However, since commercial eggs are typically collected soon after being laid and refrigerated promptly, they are typically not fertilized and won’t develop into chicks, even if incubated.

I hope this clears up any questions you might have had about egg candling. Feel free to drop more questions in the comments section!

Final Tips for Successful Egg Candling

Remember to handle eggs gently and don’t candle too frequently as it may interfere with the chick’s development. Patience is key in the art of egg candling.

Candling is a unique experience that brings you closer to your flock, even before they’ve hatched. As a chicken raiser, it’s a skill you’ll definitely want in your repertoire.

For further reading, I recommend the Complete Guide to Incubation and Hatching for comprehensive information.

Remember, every egg tells a story; you just need to learn how to read it.

Have you tried egg candling yet? Share your experiences in the comments below!

2 thoughts on “Understanding Egg Candling: A Detailed Look at Chicken Embryo Development”

  1. I only have two 6 month old hens and two roosters (supposed to all be hens, but….) One hen has been laying eggs since Halloween, so 15 days as of this writing. I have 12 eggs in this little incubator I bought, and I also got a candler. I put the first week’s eggs in on Nov 6 and the second batch of 5 in on Nov 12. My lovely yellow hen is laying an egg a day (she missed one day when I was moving their hutch.) I candled them the first day in the incubator, they were all clear. Day 6, they all had a distinctive dark spot. I added water today and had to clear the rotator (which was sticking) so I went ahead and candled again. The first 7 were largely dark with the same dark spot, but I haven’t seen any veins. Or movement. I wasn’t sure if they were fertilized at first, but I figured out, yep. I’m not sure they’re still growing, but I’m going to continue as if I am sure they are. I ordered a more professional (stronger) candler. I ordered a very inexpensive incubator and a really cheap candler. I should have the new candler in a few days and I should be able to tell the difference. I hope. Wish me luck!

    • I wish you luck, Robyn!

      I’m with you on proceeding as if they are fertile and growing. With two roosters you are assured of having fertile eggs. Just take care to not let the roosters hurt your hens if you know what I mean.

      Your incubator doesn’t have to be expensive to get good results. Just keep an eye on your temp and humidity, and keep turning the eggs at least three times a day if you can.

      I’d love to hear back from you about your hatch, either in these comments or at Dave@chickenmethod.com

      Take care, Robyn!


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