What Is Candling Method?

What is Candling?

Candling is a method of determining the fertility and development of eggs by illuminating the interior. It involves shining a bright light through the egg shell to observe the growth within. The technique dates back centuries, with the earliest known references to candling found in ancient Chinese texts from the 14th century. Candling allows poultry farmers and backyard chicken owners to check the progress of embryos and identify infertile eggs or development issues before incubation is complete.

The name “candling” comes from the original practice of using an oil lamp or candle to shine light through the egg shell. The principle is the same today, although modern candling devices use electric lights for better illumination. When candled, a fertile egg will show a network of veins radiating from the embryo, along with a distinct air pocket at the broad end. Clear, infertile eggs appear almost completely translucent, while embryos and blood vessels produce foggy shadows when backlit. By candling periodically during incubation, poultry raisers can monitor growth and mark any eggs that fail to develop normally.

In summary, candling is the process of shining light through an egg to observe interior quality and embryonic development. The technique has been used for centuries to assess fertility and catch issues during incubation. Candling allows farmers and hobbyists to gauge the progress of hatching eggs without cracking them open.

How Candling Works

Candling works by using a bright light source to illuminate the interior of an egg. This allows the user to visually inspect the egg for signs of fertility and embryonic development. When candling an egg, the shell becomes translucent and acts like a window into the egg.

There are two main things a person looks for when candling an egg. First, they check for signs that the egg has been fertilized and an embryo is developing. A developing embryo will appear as a dark spot or network of veins inside the egg. Infertile eggs will have no such signs and appear empty inside.

Second, candling allows the user to identify clear or rotten eggs. A clear egg has a consistent orange-yellow glow, while a rotten egg appears dark or mottled. By candling eggs, incubating hens can quickly identify and remove any infertile or rotten eggs before incubation.

Overall, candling utilizes light to provide valuable information about what’s happening inside an egg without having to break it open. This non-invasive technique is an important tool for monitoring egg fertility and development.

Candling Equipment

There are a few main pieces of equipment used for egg candling:

Light Sources

The most basic candling light source is a bright flashlight or penlight. However, for easier and more convenient candling, specialized lights have been designed. Candling lamps provide bright, focused illumination optimal for seeing inside eggs. These lamps often use LED or halogen bulbs. Some candling lights are designed to illuminate entire trays of eggs at once (https://layinghens.hendrix-genetics.com/en/articles/egg-candling/).

Candling Boxes

Candling boxes allow eggs to be candled in a controlled environment without outside light interfering. The boxes are specially constructed to direct light through the egg. Many have a hole on top where the egg is placed and a viewing window on the side. Advanced candling boxes may incorporate the light source itself (https://www.alibaba.com/showroom/egg-candling-equipment.html).

Handheld Candlers

Handheld candlers combine the light source and viewing window in one device. These allow conveniently candling eggs by hand. The egg is placed on the viewing window while the light illuminates from the top or side.

When to Candle Eggs

The best time to candle eggs is after they have been in the incubator for 7 to 10 days. The embryo is very fragile during the first week so it’s best not to disturb the eggs too much during this time (source). After 7-10 days, candling allows you to check on the development of the embryo and look for signs of fertility.

It’s recommended to candle the eggs a second time during days 14-18 of incubation. At this stage, you should be able to see the embryo much more clearly as well as the network of blood vessels. Candling a second time allows you to confirm the ongoing development and check for any issues like dead embryos (source).

Candling at regular intervals during incubation allows you to monitor changes over time. Comparing the candling results from early, middle, and late incubation enables you to ensure proper development of the embryo.

What to Look for When Candling

When candling eggs, there are a few key things to look out for:

Signs of fertility – In fertile eggs, after a few days of incubation you may see a small dark spot or a network of blood vessels indicating that an embryo is developing. The vessels will start to spread out as the embryo grows.[1]

Embryo development stages – As the embryo develops, it will become larger and more visible. You can track the progress day-by-day and see the embryo and its major structures as it matures.

Identifying clear/infertile eggs – Eggs that are completely clear with no veins or embryo are infertile. These eggs should be removed so they don’t explode and damage other eggs.[2] The egg may also just contain the yolk, albumen and no blastodisc or embryo.

Interpreting Candling Results

Interpreting the results of egg candling requires some knowledge and experience. There are a few key things to look for:

Assessing embryo growth – In the early days of incubation, you should see a small dark spot inside the egg which is the developing embryo. As the embryo grows over the incubation period, the air sack at the large end of the egg will get larger as the embryo uses up albumen and yolk for nourishment. The dark area should increase in size and veins surrounding it may become visible as the cardiovascular system develops.

Troubleshooting development issues – If embryo growth seems to stall or regress, the eggs may be infertile or have experienced a developmental issue. Look for signs like blood spots, odd shapes, or unexpected colors which could indicate problems. Troubleshoot incubation conditions like temperature and humidity which may need adjustment.

Deciding whether to discard eggs – Eggs that show no signs of embryo development after several days of incubation can likely be discarded. Clear eggs with no veins or dark spot present are likely infertile. Eggs with odd shapes or colors often signify issues, and these can also be discarded in most cases to avoid contaminating other eggs. Only discard questionable eggs after several candling sessions spanning 5-7 days at least.

With practice reading candling results, you will get better at determining fertility and development issues. Resources like this guide can help interpret what you see while candling. Remember that some uncertainty is normal – candling is as much an art as a science.

Candling Other Egg Types

The candling technique can be used on eggs from various species besides chickens, including ducks, geese, quail, and more. However, there are some adjustments in technique and considerations for different types of eggs:

Duck eggs have thicker shells and are more translucent than chicken eggs when candled. It can be harder to see the embryo, so candling at a younger stage around 7-10 days can be more effective (Metzer Farms).

Goose eggs need to be candled in a very dark room as their shells are quite thick. Rotate the egg continuously to detect any shadows or movement that may indicate an embryo (Metzer Farms).

Quail eggs can be candled starting at day 3 of incubation due to their small size. Look for a network of veins beginning to develop (Metzer Farms).

For any species, candling daily during the expected hatch window (typically the last 3 days of incubation) is important to identify pipped eggs and avoid rotting eggs from exploding in the incubator.

Advantages of Candling

Candling eggs offers several key benefits for poultry farmers and backyard chicken owners:

Identify infertility early – One of the main reasons for candling eggs is to identify infertile eggs that will not hatch. This allows the removal of these eggs from incubators early on, saving time and electricity costs. According to The Poultry Shop, candling helps “identify infertile eggs that should be removed from the incubator” (source).

Monitor embryo growth – Candling allows checking on the development of embryos inside fertilized eggs. It enables monitoring if the embryo is growing properly during incubation. Any embryo development issues can be identified.

Troubleshoot incubation issues – Observing embryo growth through candling may reveal incubation problems. Underdeveloped embryos may indicate incorrect incubation temperature or humidity. Candling lets poultry farmers diagnose and troubleshoot these issues.

Disadvantages of Candling

While candling can provide useful information about what is going on inside an egg, there are some potential downsides to be aware of:

Requires time and effort – Candling eggs takes time and effort to do properly. Each egg must be carefully candled and assessed, which can become tedious when candling large batches of eggs. This extra time commitment may not be practical for all poultry keepers.

Can harm embryos if done improperly – The embryo inside the egg is delicate, especially in early stages of development. Excessive shaking, jostling, or exposure to light/heat during candling can potentially harm the growing embryo. Proper candling technique is important.

Not 100% definitive – While candling can identify many clear/infertile eggs, it does not provide completely definitive results in all cases. It takes some experience to accurately interpret candling. There is still a chance some fertile eggs may be misidentified.

According to research from Brinsea (https://www.brinsea.com/brochures/EggCandling.pdf), candling should be done quickly and infrequently to minimize disturbance to the embryo. However, when done carefully and properly, candling is considered safe for the developing chicks.

Alternatives to Candling

While candling is a popular and trusted method for checking egg fertility and development, there are some alternatives that may work better in certain situations:

Other methods to assess fertility include:

• Floating eggs in water – fertile eggs will tip upwards while infertile eggs will lay flat
• Cracking eggs open after a period of incubation to check embryo development
• Listening to eggs with a stethoscope for heartbeats after 5-7 days of incubation

There are also some high-tech options like the Egg Buster fertility checker that uses infrared light and sensors to detect an embryo inside an egg. Tools like these can give quick, accurate results.

Candling may not be the best method if you need to frequently check large quantities of eggs. The process can be time consuming and you risk harming the embryo by over-handling the eggs. In these cases, an automated fertility checker may work better.

Overall, while candling remains a simple, low-cost way to check egg fertility, there are some alternatives that can be used instead depending on your specific needs.