Does moving the egg during candling damage it? No, as long as you're careful and as long as you don't candle after day 18 of incubation. You will generally need to turn the egg to see what's going on inside, particularly as you come to the later stages of incubation. Always take it slowly.
Healthy embryos will respond to the light by moving. Sometimes the movement is very sluggish and it can take 30 to 40 seconds for the embryo to move when held under the candling lamp. This indicates the embryo is not healthy and the egg should be discarded.
By being able to identify and remove non-viable eggs (infertile or early death) you can also avoid the risk of a rotten egg exploding and contaminating your hatch with dangerous germs. And candling does not harm your eggs.
It's important that you do not candle every day so as to not disturb the growth and development. Also, avoid using eggs that are dirty or soiled in any way. Never leave eggs outside the incubator for more than half an hour.
Over-handling, e.g. over-candling, will increase the potential of an egg getting contaminated from dirty hands, a sneeze or anything else! Contaminated egg shells create dead chicks or an egg that could explode in the incubator!
And before day seven there isn't much to see, anyway. After candling on day seven, you can wait another week and candle again on day fourteen. Avoid candling from day sixteen or seventeen up until the eggs hatch, as moving or shifting eggs this late in development could harm them.
If the egg is rotten, you'll be able to see dark spots or discoloration, and the contents may appear cloudy. It's important to note that not all abnormalities found during the candling test indicate that the egg is rotten.
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.
Candling Results
The embryo appears as a dark spot which becomes larger as the incubation period continues. and incubation continues will grow larger until light will only pass through the air cell end of the egg.
After a week of incubation, if an egg is fertile, you will see the embryo starting to develop as a dark spot with spider-like veins stretching out around it. Sometimes it isn't possible to observe the embryo if it's in the centre of the egg or if the eggshell is thick or a darker colour.
Signs of development will typically appear as a dark spot surrounded with numerous blood vessels. If this is what you see, then congratulations, your egg is viable and contains a chicken embryo. An unfertilized egg will not show any development at this stage and will simply appear clear when candled.
If you're fortunate enough to have light-shelled eggs, from about day 5 you'll start to see tiny spider like markings appearing in the yolk area when you candle your eggs. In a dark-coloured egg like the Marans or Welsummer, they're much more difficult to spot.
If there are dead nestlings or unhatched eggs in an “active” nest (one that also contains living eggs or young) then it's best to leave them in the nest until the other young fledge to reduce disturbance.
Quitters — When embryos stop growing, we call them "quitters." You will see a thin, blood ring around the yolk. Quitters are removed from the incubator and thrown away. If you want to view the embryo, have your parent or teacher help you open the egg. Be sure to wash your hands afterwards.
An egg candler is a small handheld device that shines a bright light through the eggshell, allowing you to see the inside of the egg. If the embryo is still alive, you should be able to see blood vessels and movement inside the egg. However, if the embryo has died, you may see no movement or blood vessels.
Day 15. What is this? You can see here how the embryo is now filling a large part of the egg. Candling at this point provides a view of the vein - just above the air cell - moving quite energetically as the chick positions itself for hatching.
Shine a bright flashlight through the egg in a dark room, and look closely at the inside. If the egg is alive you will see veins running through it. The process of removing dead or rotten eggs during incubation that uses this method is candling.
After 21 days in the incubator, the chicks should hatch from the eggs. Try not to help the chicks hatch, as they develop muscles during the hard work of hatching from their eggs. The egg will start to wiggle around a bit as the chicken inside works to open the egg.
Even though most hens will get this right, it is still possible that some embryos will die and the eggs will rot, or there will be eggs that aren't fertile. Your broody hen will usually be able to tell if an egg is rotten, and she is likely to push it out of the nest; however, it's an idea to candle the eggs.
Candling is when you shine a bright light through an egg to illuminate its contents. It gives you a good idea of an embryo's development. Don't candle eggs after Day 17 as any movement can harm the chick.