How should you candle an egg to check for viability?

Candling eggs, once involving candle flames, is now a standard practice. Knowing how should you candle an egg is vital for monitoring embryo development and removing non-viable eggs to ensure successful hatching.

Quick Summary

Candling eggs helps determine which eggs are viable during incubation. Using a bright light in a dark room allows one to see the embryo's condition to manage the hatching process.

Key Points

• Start Around Day 7: The first candling should happen about a week into incubation to check for development.

• Use a Bright LED Light: Use a cool LED light source to see inside the egg without heat damage.

• Look for Blood Vessels: A healthy embryo appears as a dark spot with spider-like blood vessels.

• Remove Non-Viable Eggs: Remove infertile or dead eggs to prevent contamination.

• Handle with Care: Always wash hands before handling and keep the egg removal time to a minimum.

• Adapt for Dark Eggs: For dark-shelled eggs, use a very bright light, as visibility will be limited.

What is Egg Candling?

Egg candling is a non-invasive technique to inspect an egg's contents using a bright light. This method enables the checking of fertility, the monitoring of the embryo's development, and the identification of eggs that have stopped developing. Removing infertile or dead eggs prevents them from rotting and potentially exploding in the incubator, which can contaminate healthy eggs. While historically candles were used, modern LED light sources are more effective and safer for the embryos.

Essential Equipment for Candling

To begin candling, you will need a few simple items, with the most important being the candler itself. Dedicated egg candlers are available, though many find a high-lumen, cool-light LED flashlight works well.

• Light source: An LED flashlight is ideal because it is bright and doesn't produce much heat, which is important for the embryo. Rechargeable models are great for consistent brightness.
• Dark room: A completely dark, or dimly lit, room is essential for seeing through the eggshell.
• Clean hands: Wash hands before handling eggs to prevent bacteria transfer.
• Incubator access: Be prepared to work quickly to minimize how long the eggs are out of the incubator, which helps maintain stable temperature and humidity.

How to Candle an Egg: Step-by-Step

Here is a simple, effective procedure for candling your eggs:

1. Thoroughly wash and dry hands.
2. Move to a dark room.
3. Gently remove an egg from the incubator and hold it carefully, handling it as little as possible.
4. Place the large end of the egg against the candling light. The air sac is at this end, making it the easiest part to illuminate.
5. Cup your hand around the egg and the light source to create a tight seal, blocking any escaping light. This maximizes visibility.
6. Rotate the egg slowly and carefully to examine the entire contents. Tilt it to get the best view.
7. Observe the interior for development signs. Look for the embryo as a small, dark spot with spider-like blood vessels. In later stages, movement may be seen.
8. Return the egg to the incubator promptly to minimize heat and humidity loss.

A Timetable for Candling Success

Candling is most effective at specific intervals during incubation, which is about 21 days for a chicken egg.

• Day 7: This is the first recommended candling session. A small, dark spot (the embryo) with tiny, red blood vessels radiating out should be visible. If the egg is infertile, it will appear clear. Re-check in a few days if unsure.
• Day 14: By this point, a healthy chick will fill much of the egg, making the interior darker and less transparent. Movement might be visible. Remove any cloudy or undeveloped eggs. A 'blood ring' indicates early embryo death.
• Last few days: Candling after day 17 is generally not recommended, as the chick is preparing to hatch. The egg is mostly opaque with only the air sac visible.

Interpreting Your Candling Results

Observation on Day 7	Status	Action	Notes
Clear with yolk shadow	Infertile	Remove	No development has occurred.
Dark spot with red veins	Fertile, developing	Return to incubator	Indicates healthy embryo growth.
Dark ring around contents	Early death	Remove	The embryo began developing but has died.
Cloudy, swishy contents	Dead embryo	Remove	Indicates an embryo that died a bit later.
Hairline crack in shell	Unviable	Remove	Bacteria can enter and contaminate the egg.

Candling Dark-Shelled Eggs

Dark-shelled eggs, such as from Marans or Welsummers, are harder to candle because less light penetrates the shell. For these eggs, a bright light source and a completely dark room are required.

• Wait a few extra days: Waiting until day 10 or later for the first candling can help, giving the embryo more time to develop.
• Use a focused, high-intensity light: A powerful LED light is a must. Cup hands tightly around the egg to prevent light leakage.
• Compare with a known good egg: Have a light-colored egg for comparison to adjust your eyes to what a healthy egg looks like.

Conclusion: Maximizing Your Hatch Rate

Following these candling guidelines can increase the chance of a successful hatch. Candling is about monitoring progress and ensuring the best environment for chicks. With practice, identifying a viable embryo becomes easier, allowing for confident management of the incubation process, and reduces the risk of contamination. Consistency and careful handling are key. Consult resources like the University of California Agriculture and Natural Resources catalog for more detailed information.

Frequently Asked Questions

Can candling an egg harm the embryo?

No, candling will not harm the embryo if done correctly and quickly. The light from an LED is cool, and brief exposure will not affect development if it is not overheated or kept out of the incubator for too long.

What is the best light source for candling eggs?

A modern, high-lumen LED flashlight is the best light source. It provides a strong, focused beam without generating excessive heat, which is safer for the developing embryo.

What does an infertile egg look like when candled?

An infertile egg will appear clear, with no signs of an embryo or blood vessels. Only the shadow of the yolk may be visible.

How can you tell if an embryo has died?

If an embryo dies early, a dark, cloudy mass or a 'blood ring' may be visible. In later stages, no movement is visible, and the blood vessels may look broken down.

Can I candle eggs right after placing them in the incubator?

It is best to wait until at least day 5-7 for your first development check. Candling too early can disturb the fragile air cell, and there is often little to see.

How do you candle dark-shelled eggs?

Candling dark-shelled eggs requires a very bright light and a completely dark room. It may be necessary to wait longer for clearer signs of development to appear.

What is the purpose of removing non-viable eggs?

Removing infertile or dead eggs prevents them from rotting and potentially exploding in the incubator, which can contaminate healthy eggs with bacteria. It also makes better use of the incubator's space.