CANDLING EGGS the step by step guide on how to candle your eggs and check fertility
Pictured above: top - how to correctly hold an egg for candling
middle: a fertilized egg being candled
bottom: the development of a growing embryo inside the shell
Understand why you need to candle your eggs. When you are hatching eggs at home, it is good practice to keep track of how the eggs are developing. However, this can be very difficult (if not impossible) without the use of candling. Candling involves shining a bright light into the egg, allowing you to see its contents and check whether it is developing properly.
- When you are hatching eggs at home, you will very rarely get a 100% hatch rate. Some eggs will not be fertile to begin with (these are called "yolkers") while others will stop developing at some point during the incubation process (these are known as "quitters").
- It is important that you are able to identify and remove these yolkers and quitters during the incubation process, otherwise they can begin to rot and eventually burst inside the incubator, contaminating the other eggs with bacteria and creating a very bad smell
Use the correct candling equipment. Candling equipment doesn't need to be very fancy or specific -- in fact, in the old days it used to be done with the flame from a candle (hence the name). The main requirement is a bright light (the brighter the better) with an opening smaller than the diameter of the eggs you intend to candle. You will need to conduct the candling in a very dark room in order to see inside the egg.
- Alternatively, you can take a very bright flashlight and cover the opening with a piece of cardboard with a hole (1 inch in diameter) in the middle
- A more high-tech, expensive option for candling eggs is known as an Ovascope. This has a rotating stand on which you place the egg. The egg is then covered by a hood which blocks out any ambient light. You can then view the egg through an eyepiece, which magnifies the egg slightly for easier inspection.
- Place the larger end of the egg (where the air sac is) directly against the light. Hold the egg near the top, between your thumb and forefinger. Tilt the egg slightly to one side and rotate until you get the best view.
- As you work, you should mark each egg with a number and take notes on your findings. That way, you can compare the results of your first candling with the results of your second candling.
- Try to work quickly, but not so fast that you risk dropping the egg. As long as the eggs are returned to the incubator within twenty minutes to half an hour, there is no risk of the candling process affecting their development. A mother hen will frequently leave her eggs for short periods of time while she is incubating them.
- Be aware that it will be more difficult to candle brown or speckled eggs as the dark shells do not become as transparent under the light.
- There will be a visible network of blood vessels spreading from the center of the egg outwards.
- With a weaker candler, you might just be able to make out the clear bottom half of the egg (where the air sac is) and the darker top half of the egg (where the embryo is developing).
- With a good candler, you might be able to see the dark outline of the embryo at the center of the network of blood vessels. You are most likely to see the embryo's eyes, which are the darkest spots inside the egg.
- If you're lucky, you might see the embryo moving!
- The main indication that an egg is a quitter is the development of a blood ring. A blood ring looks like a well-defined red circle, which is visible on the inside of the shell. It forms when the embryo dies and the blood vessels supporting it pull away from the center and rest against the shell.
- Other indications that an egg is a quitter include the development of blood spots or blood streaks inside the egg. However, these dark patches can be difficulty to distinguish from a healthy embryo at this early stage.
- If you are 100% certain that the egg is a quitter (the appearance of a blood ring is a very definite sign) then you should discard the egg immediately to prevent it from turning bad and exploding inside the incubator.
- The egg looks the exact same as it did when you first candled the eggs before putting them in the incubator.
- The inside of the egg looks fairly clear, with no visible dark spots, blood vessels or blood rings.
If you are unsure, leave the eggs alone. If you think you might have identified a yolker or a quitter, but are not 100% sure, do not discard them just yet. If you do, you run the risk of throwing away healthy eggs.
- Just make a note of which eggs have a question mark over them, then place them back in the incubator. It is always worth giving them another chance.
- Check the questionable eggs again on day fourteen. If there are still no obvious signs of development or if a blood ring has finally formed, you can discard them.
Eventually, the chick will fill almost all of the space inside the egg and the air sack will increase further in size. When the chick finally hatches, it will break through the inner membrane into the air sack to take its first breaths of air. It will crack / push through the shell with its egg tooth (attached to the end of the beak). This allows further oxygen into the air sack so the chick can continue to breathe.
Over the final 24 hours, the remainder of the yolk sack will be absorbed, this will give the chick enough energy to turn inside the shell and slowly break from the shell as it goes. It will then use its feet to push itself out of the shell.
There is little point in candling eggs during the final few days other than to check for the air sack size because you will not see much. The chick almost fills the shell.
If you assist a chick in hatching, you take the risk of removing the shell too soon, before the yolk sack has been absorbed and before the navel has healed over where the allantois was attached. High humidity in the incubator will stop the membrane from drying out, keeping it soft and easy for the chick to break out. Humidity for the last three days should be 60% - higher and you risk the chance that the chicks can drown in the shells, lower and the shells will not be soft enough for the chicks to break out.
Chicks do not need food for the first 24-48 hours after hatching thanks to the energy they get from the yolk sack, and this is why most people recommend that you leave the chicks in the incubator for this period to dry completely and also allow the humidity to remain consistent for the remaining chicks to hatch.
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