Egg Candling Guide: Master the Art of Monitoring Chick Development

Candling Eggs: A Comprehensive Guide in 2025

January 5, 2025 Ricky Jehen

Candling eggs is a valuable technique used to assess the development of an embryo inside an egg during the incubation period. By shining a bright light through the egg, you can determine its fertility and monitor the chick’s progress. This comprehensive guide will equip you with the knowledge and skills to successfully candle your eggs, increasing your chances of a healthy hatch.

What is Egg Candling?

Egg candling is a straightforward process that allows you to monitor the development of embryos inside incubated eggs. This method involves using a light source to illuminate the interior of an egg, allowing for observation of the embryo’s development and assessment of the egg’s viability.

While candles were traditionally used for this purpose, modern candling often utilizes specialized candlers or bright flashlights. This helps determine whether an egg is fertile and if the embryo is developing properly. Originally done with candlelight, modern candling uses specialized equipment or even a strong flashlight.

3 Essential Equipment!

Before you begin candling, gather the following:

Egg Candler: A dedicated egg candler is ideal for optimal illumination, but a bright flashlight or even a smartphone’s flashlight can be sufficient. You can purchase a dedicated egg candler or use a bright flashlight. Some people even use their mobile phone’s flashlight. For eggs with darker shells, a brighter light source is recommended to ensure visibility.
Dark Room: Candling is best performed in a dimly lit or completely dark room to minimize external light interference and maximize the clarity of the egg’s contents. Candling should be done in a dimly lit or completely dark room for the best visibility.
Clean Hands: Always wash your hands thoroughly before handling eggs to prevent the transfer of bacteria and potential contamination. Always wash your hands before handling eggs to prevent contamination.

When to Candle Eggs?

Candling Stage	Days of Incubation	Purpose
First Candling	7-10	Identify fertile eggs and early signs of development
Second Candling	14-18	Check for stopped development or uncertain cases

It’s important to note that while candling can be done at various stages, it’s generally recommended to limit it to two or three times during the incubation period. Excessive handling and temperature fluctuations can disrupt the delicate environment within the incubator and potentially harm the developing embryos.

First Candling (Days 7-10): The first candling should occur around 7 days after placing the eggs in the incubator. This is when you can start seeing signs of embryo development.
For the first candling, aim for around day 7 after placing the eggs in the incubator. This allows you to identify fertile eggs and observe early signs of development. Keep in mind that brown eggs, due to their darker shells, may need to be checked a bit later than white eggs. It’s crucial to avoid candling eggs too early, especially within the first 7 days, as excessive light exposure during this critical period can damage the developing embryo.
Second Candling (Days 14-18): A second candling can be done around day 14 to check for any eggs that may have stopped developing.
A second candling session around day 14 helps identify any eggs that may have stopped developing (early deaths) or those you were unsure about during the first candling. While it’s generally best to avoid candling after day 18 as the chicks prepare to hatch, some people choose to recheck eggs when they stop turning them a few days before hatching.
Avoid Candling After Day 18: Do not candle after day 18, as this is when chicks are preparing to hatch and should not be disturbed.

Candling Procedure

Follow these steps for a successful candling experience:

Prepare Your Space: Ensure you are in a dark room with your candler ready and have your candler ready. Ensure any necessary materials, such as a clean egg carton or a soft-lined basket, are available to safely manage the eggs during the process.
Position the Egg: Gently hold the egg against the light source with the larger end (where the air sac is located) facing the light. This allows for better illumination and observation of the egg’s interior. Hold the egg with the larger end (where the air sac is located) against the light source. This allows you to see inside more clearly.
Observe the Contents: Carefully examine the egg’s contents, noting the following:
- Fertile Eggs: A fertile egg will show a dark mass (the embryo) with a network of blood vessels radiating outwards. You should see a dark mass (the embryo) surrounded by blood vessels. You might even observe slight movement or a beating heart.
- Infertile Eggs: An infertile egg will appear clear with no visible embryo or blood vessels. If the egg appears clear with no visible structures, it is likely infertile. The yolk may be visible as a shadow.
- Dead Embryos: An egg with a dead embryo may show a dark mass without blood vessels or a distinct dark ring. Eggs that have died will show a dark mass without blood vessels or may have a distinct dark ring.
Limit Handling Time: Keep the egg outside the incubator for no more than 5-10 minutes to maintain optimal temperature and humidity levels. Keep the egg out of the incubator for no more than 5-10 minutes to maintain temperature and humidity levels.
Document Your Findings: Maintain a record of each egg’s development to track progress and identify any non-viable eggs that need to be removed. Keep records of which eggs are developing well and which ones are not, so you can remove any non-viable eggs promptly.

Tips for Successful Candling

Practice on Unfertilized Eggs: If you’re new to candling, practice on unfertilized eggs to gain familiarity with the process and avoid accidentally damaging fertile eggs. If you’re new to candling, practice on unfertilized eggs to get comfortable handling them without causing damage.
Use a Bright Light for Dark Shells: Darker eggshells can be harder to see through, so use a brighter light source and be patient as you examine the egg’s interior. Dark-shelled eggs can be harder to candle; use a brighter light source and be patient as you try to see inside.
Don’t Overdo It: Limit candling sessions to two or three times during incubation to avoid unnecessary disturbance to the developing embryos. Limit your candling sessions to two or three times throughout incubation to avoid disturbing the eggs unnecessarily.

What to Look for During Candling

A useful guide from YouTube:

First Candling (Days 7-10)

Fertile Egg: You should observe a small dark spot (the embryo) with a network of blood vessels radiating outwards. The embryo may exhibit slight movement when you rotate the egg.
Infertile Egg: The egg will appear clear with no signs of development. You might see the yolk’s shadow, but there will be no embryo or blood vessels.

Second Candling (Days 14-18)

Healthy Embryo: The embryo will appear larger and more defined, with a clear network of blood vessels. The air sac at the larger end of the egg should be noticeably bigger.
Dead Embryo: A dead embryo may appear as a dark mass without blood vessels or a blood ring. The blood vessels may appear broken down or as streaks under the shell.

Troubleshooting with Candling

Candling can also help identify potential problems beyond just fertility. For example, a “dead in shell” chick may be identified by a yellow and sickly appearance of the egg contents, with blood vessels that are no longer fresh and may have turned brown.

Candling with a Smartphone Flashlight

While a dedicated candler is generally recommended, a smartphone flashlight can be an effective tool for candling, especially for eggs with lighter-colored shells. Ensure the flashlight is on its brightest setting and hold it directly against the egg in a dark room. Some people find it helpful to create a makeshift stand for the phone to stabilize the egg and prevent accidental drops. However, for those who plan to candle eggs regularly, especially those with dark shells, investing in a dedicated candler is worthwhile for its superior illumination and ease of use.

Signs of a Healthy Embryo

A healthy developing embryo typically exhibits the following characteristics during candling:

Movement: The embryo should move in response to the light, indicating it is alive and active. Sluggish movement can be a sign of a weak or unhealthy embryo.
Well-defined blood vessels: Healthy embryos have a clear and intricate network of blood vessels that appear reddish in color.
Growth: The embryo should grow larger and more defined over time.
Increasing air sac size: The air sac at the blunt end of the egg should gradually increase in size as the embryo develops and consumes the egg’s contents.

What to Look for Before Incubation

Even before incubation begins, candling can provide valuable insights into the potential fertility of an egg. On day 1, a fertile egg will exhibit a lemon-yellow yolk with a very small, dark circle in the center. This small circle represents the hen’s contribution to the egg’s viability. If this circle is absent, the egg is likely infertile.

Early Development (Days 5-6)

Around days 5-6 of incubation, a fertile egg will show a small red dot (the embryo) about the size of a match head, surrounded by faint blood vessels. This early candling can help confirm fertility and identify any eggs that may not be developing properly.

Conclusion

Candling eggs is a valuable skill for any poultry keeper. By understanding the process, knowing what to look for, and following the guidelines outlined in this guide, you can monitor the development of your chicks, identify potential problems, and significantly increase your chances of a successful hatch. Remember to handle the eggs gently, limit candling frequency, and maintain a clean and controlled environment within your incubator for optimal results. Candling not only allows you to identify fertile eggs and monitor embryo development but also helps you troubleshoot potential issues, ensuring the health and viability of your future flock. By following these steps and tips, you’ll gain confidence in your ability to candle eggs effectively, helping ensure a successful hatching process.

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