Candling is the process of observing the embryo development inside of an egg holding a strong light above or below the egg. A candle lamp consists of a strong electric bulb covered by a plastic or aluminum container that has a handle and a hole. The egg is placed against this opening and illuminated by the light. If you don't have a candle lamp, improvise. Try using a flashlight.

Lighting is carried out in a darkened room or in an area shielded by curtains. Figure 6 shows the light booth at the John Francis Virology Laboratory.

Determination of embryo viability:
Under a candle lamp, the embryo appears as a dark shadow with the head as a dark spot. Healthy embryos will respond to light by moving. Sometimes the movement is very slow and the embryo may take 30 to 40 seconds to move when held under a candle lamp. This means that the embryo is not healthy and the egg should be discarded.

Look closely at the blood vessels. In a healthy embryo, they are well defined. After the embryo dies, the blood vessels begin to disintegrate. When viewed under a candle lamp, they then appear as stripes under the shell. Translucent light also reveals cracks in the eggshells. Eggs with a cracked shell should be thrown away.

Infertile eggs: They are easy to detect because the egg is clear. Eliminate

Premature deaths: The embryo developed for several days and then died. Candling will reveal a small dark area and disrupted blood vessels. Often the deteriorating blood vessels appear as a dark ring around the egg. Eliminate.

Late deaths: Often difficult to distinguish from a viable embryo at the same stage of development. Look for absence of movement and disintegration of blood vessels. Eliminate

Viable embryos: They move in response to light and have well-defined blood vessels. Mark the air bag and the inoculation site, then return the eggs to the incubator ready for inoculation.