Jessie Taylor
Candling is the process of checking the viability of an egg by observing its contents. This is done by illuminating the egg with a light source, traditionally a candle, in a darkened room. It is recommended to candle eggs after 7 days of incubation to check for signs of a viable embryo, and again at 14 days to remove any non-viable eggs. Some sources suggest candling at 18 days, but it is generally advised to avoid candling during the last few days before hatching. The frequency of candling can vary, but it is important to minimise the time eggs are out of the incubator and to handle them carefully to avoid damaging the embryos.
| Characteristics | Values |
|---|---|
| Days before candling eggs | 3, 7, 8, 10, 14, 18, 21 |
| Reasons for candling | To check for cracks, viability of the embryo, veins, blood spots, embryo movement, air sac size, and signs of non-development |
| Equipment | Basic flashlight, ovascopes, Brinsea candlers |
| Time taken | As little time as possible, ideally a few minutes |
| Frequency | Every day, or every few days |
| Egg positioning | More pointed end facing down, occasionally blunt end down for a clearer view |
| Lighting | Dark room or closet |
| Egg turning | Stop turning chicken eggs at 18 days, and duck eggs at 25 days |
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Embryo development
Day 3 to Day 6
On day 3, veins may start to become visible, indicating the initial stages of embryo development. By day 5, a tiny dot representing the embryo can be observed, along with veins radiating outward. However, it is important to note that eggs should not be held for more than 6-7 days before incubation, as it decreases the chances of fertility.
Day 7
Candling on day 7 is crucial. By this time, the embryo should be visible as a dark spot, with spider-like veins extending from it. If the egg is clear, with no signs of development, it is considered a "yolker" and will not develop further. In some cases, the embryo may have started developing but then experienced early embryonic death, resulting in a thin ring around the inside of the egg. These non-viable eggs should be removed.
Day 8
Around day 8, the embryo becomes more active, and you may observe the “peep” wiggling and kicking inside the egg.
Day 14
Candling is recommended again on day 14. By this stage, the embryo would have grown significantly, and any eggs with non-viable embryos should be removed to prevent the risk of a rotten egg exploding.
Day 18
Candling on day 18 is critical. It is the last opportunity to check the development of the embryos before the “lockdown” period leading up to hatching. Any eggs showing signs of non-development should be discarded to prevent bacterial contamination in the incubator.
Day 21
On day 21, the baby chick is fully developed and ready to hatch. Throughout the 21-day incubation process, careful candling and monitoring of embryo development are essential to ensure a successful hatch.
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Optimal timing
After seven days of incubation, you can be reasonably precise about the viability of the embryo. You should candle eggs again at 14 days of incubation to check for any embryos that have died and remove them to lessen the risk of a rotten egg exploding. At 14 days, veins should be visible regardless of egg colour.
You can candle eggs again after 18 days of incubation, but this is not recommended as the chick will be positioning itself, ready to emerge. By this stage, the embryo takes up most of the egg and appears as a dark area within the egg.
Some people candle eggs during the last few days before they hatch if they are concerned about humidity or having hatching problems. However, it is best to avoid candling eggs during the last three days of a hatch unless you have a specific reason to do so.
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Incubator humidity
Candling eggs is the process of shining a bright light through the egg in a dark room to check for fertility and embryo development. It is recommended to candle eggs after 7 days of incubation and again at 14 days. After a week of incubation, one can reasonably determine the viability of the embryo. At 14 days, non-viable eggs can be removed to reduce the risk of a rotten egg exploding.
During the first 18 days of incubation, the minimum humidity should typically be maintained between 35% and 45%. This range allows for the proper development of the air cell in the eggs. Insufficient humidity during this period can cause the eggs to dry out, making it challenging for the chicks to hatch.
In the final days of hatching, known as the lockdown phase, humidity should be increased to aid the chicks in breaking out of their eggs. The ideal humidity range during lockdown is generally around 60% to 75%. While higher humidity is suitable for this phase, maintaining 75% humidity throughout the entire incubation period can lead to issues such as drowning.
To ensure successful hatching, it is recommended to increase humidity to 65% to 70% during the last 3 days of incubation. This increase in humidity assists the chicks in their final preparations for hatching.
Several signs indicate that the humidity levels in the incubator are too high. Condensation is one of the most visible indicators, where droplets of water may appear on the walls, eggs, or window inside the incubator. High humidity can also affect the eggshell's condition, making it damp or sweaty. This excess moisture can compromise the integrity of the eggshell, making it more difficult for the chick to break through during hatching.
To manage and monitor humidity levels accurately, it is advisable to use a hygrometer, a device specifically designed to measure humidity. By tracking the humidity conditions in the incubator, one can make any necessary adjustments to maintain the optimal range for successful embryo development and hatching.
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Egg viability
Egg candling is a process used to assess the fertility and development of eggs during the incubation period. It involves shining a light through an egg to observe its internal contents, allowing handlers to identify clues about its viability, such as the presence of a developing embryo, signs of early mortality, or infertility.
The timing of candling can vary, but it is typically performed at several points during the 21-day incubation process. Some sources suggest candling as early as day 5 or 6, while others recommend waiting until day 7 to allow for better precision in determining embryo viability. Candling can also be done on day 9 or 10, and again closer to the day of transfer to the hatcher, usually around day 18. However, it is recommended to minimise the number of candlings to avoid disrupting the incubator's humidity levels.
During candling, handlers look for specific indicators to determine egg viability. A clear egg, or one with a thin ring and an irregular-looking lining, indicates that the embryo is no longer viable. Dead embryos will appear as a murky, dark shadow. Fertile eggs, on the other hand, will show a dark spot surrounded by numerous blood vessels, which some describe as resembling a "spider". As the embryo grows, the air pocket in the egg should increase in size, and the egg will become darker.
By day 14, viable and developing eggs become more challenging to candle as the chick takes up most of the egg. At this stage, the dark spot will appear cloudy, and the number of blood vessels will have increased compared to day 7. Additionally, by day 18, the embryo has typically developed into a chick, and candling is crucial to ensure none of the eggs have died.
Overall, egg candling is an essential step in ensuring the highest possible hatch rates, optimising hatchery operations, and producing healthy chicks. It allows handlers to identify and remove unviable eggs, preventing them from exploding and spreading bacteria within the incubator.
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Potential issues
Candling eggs is a straightforward process that involves shining a bright light into an egg to see its contents. While candling is generally considered safe, there are some potential issues to be aware of.
One issue is that candling may not always provide an accurate assessment of egg viability. For example, during the later stages of incubation, it can be difficult to distinguish between a viable embryo and an embryo that has died. This is because the blood vessels in a dead embryo may still appear intact for a period of time. As a result, it is possible that a viable embryo could be mistakenly discarded.
Another issue is that frequent candling can disrupt the incubation process and potentially harm the developing embryos. Eggs should not be kept out of the incubator for an extended period, and it is important to maintain the temperature of the eggs during candling. Additionally, oil from hands can clog the pores in the eggshell, restricting oxygen flow to the embryo. Therefore, it is recommended to handle the eggs as little as possible and only remove them from the incubator for a short time during candling.
Candling with an open flame, such as a candle, can also pose a fire hazard if not done carefully. While this method is less common today, it is important to note that using an open flame for candling requires extra caution.
Furthermore, candling may not always detect all cracks or defects in eggshells. Hairline cracks or small defects may be difficult to see, even with a bright light. As a result, cracked eggs may go unnoticed, leading to potential bacterial infections and embryo death.
Finally, candling eggs can be time-consuming and may require some practice to interpret the results accurately. It is important to have a basic understanding of embryology and the normal development of eggs to make informed decisions based on candling observations.
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Frequently asked questions
It is recommended to candle eggs after 7 days of incubation and again at 14 days.
If the egg is infertile, you will only see the yolk's shadow inside without any spider-like veins or an embryo.
By day 7, you should be able to see a small embryo forming with spider-like veins. By day 8, you may be able to see the chick wiggling and kicking in the egg.
Eggs can be out of the incubator for up to 30 minutes, but it is recommended to put them back as soon as possible to avoid chilling.
You can candle eggs every day if desired, but it is generally done at specific intervals, such as days 7, 14, and 18, to check on the embryo's development and viability.
