Candling is simply the process of shining light into the bottom of an incubated egg to see the contents and determine whether the egg is fertile. Light is shone up into the egg from the base and by doing this the egg becomes transparent and the contents can be seen. Please note at this point if you are hatching olive or dark brown eggs it is sometimes impossible to candle as the contents cannot be seen. If this is the case simply leave the eggs in the incubator and cross your fingers! Candling can be as simple as shining your mobile phone torch into the egg.
So candling your incubated eggs at certain stages of the process is important so you can disregard any infertile eggs or eggs where the embryo has died. This gives you some idea of how many chicks you can expect from your hatch and allows any eggs that do not make the grade to be taken out of the incubator.
This blog post is really simple and straight forward and doesn't go into lots of details (we'll do that later) but simply allows you to learn the basics.
When I first started candling eggs it was a total mystery and I thought it was really complicated but when you know what you are looking for it is quite simple. Here's some advice to help you that I learnt on my journey of egg candling.
Don't candle your eggs to early. Advice is to candle day 7 at the earliest.
My first piece of advice is not to candle your eggs too early. When I first started hatching I was addicted to candling! I spent hours candling. Every few days I would shine my torch and mark the progress of my beloved eggs. You have to remember that it's not natural for light to be shone into an egg and candling in the first 7 days can actually damage the embryo. Plus from a total novice viewpoint you don't really know what you are looking for and the signs can be easily confused. If you candle day 7 there is no mistaking the good eggs from the bad.
So at day 7 you have 3 scenarios.
1: YOUR EGG IS NOT FERTILE.
So scenario one is that your egg is unfortunately infertile. The sperm didn't fertilise the egg and if this is the case you need to take these eggs out of the incubator. At day 7 infertile eggs are easy to tell. They are empty. You will see a yolk floating around but you won't see an embryo or any blood vessels. It will look similar to this and these eggs can be removed from the incubator.
2: YOUR EGG WAS FERTILE BUT THE EMBRYO DIED.
This can be a common one especially with eggs that has been through the postal system. Embryos are complex things and there is no one reason why some don't make it, it's just nature and means something wasn't right. If the embryo has died you won't see any blood vessels. In some cases you might just see a black blob like this:
There is no life to it and unfortunately this embryo didn't make it and needs to be taken out the incubator. In some cases you get what's called a blood ring. This indicates infection and also that the embryo and blood vessels have dispersed and died.
Again if this is the case then these eggs need to be removed from the incubator. Right onto scenario 3 and good news!
3: YOU HAVE A HEALTHY EMBRYO.
Hooray the good news that your baby is developing nicely. On candling you will see a dark spot and then spider like blood vessels slowly and surely spreading throughout the egg. This is a sign of a healthy egg that is developing as it should. After seeing a healthy day 7 embryo it becomes a lot easier to spot the ones that haven't made it. Here's an example.
One piece of advice is that if you are unsure just leave the egg in the incubator. It won't harm the other eggs as long as there are no cracks in the shell. That's the one thing to look out for, and you can normally smell it before you see it, a rotten egg. It's rare you get one but if it explodes it can infect the other healthy eggs. Just look for cracks and if anything is oozing take it straight out this is not normal.
When to candle next?
So I would initially candle at day 7 and then I would leave the eggs in the incubator until day 18. So i only candle the eggs twice, this allows the eggs to be left alone to grow without interference. At day 18 (for chickens, day 25 for ducks) we lock down the incubator (click here for details of what that means) and this is the last chance we can candle the eggs and see which will hopefully hatch. At day 18 you will see a big difference, the chick will be getting ready to hatch, you will see movement and a large air sac ready for the chick to break through and take it's first few breathes. If the embryo has died between day 7 and 18 it will show no signs of movement and no signs of healthy blood vessels. If in doubt leave it in the incubator. If your fears are confirmed it simply will not hatch. Here is an example of a healthy embryo at day 18.
So during lock down it's vital that you don't go into the incubator at all. Every time you lift the lid humidity is lost and can massively affect the chicks hatching. If you have live chicks at day 18 please remember this does not guarantee a live chick but the percentages are definitely in your favour.
I hope this blog has helped first time hatchers. We will go into more details in other blog articles. Happy hatching and try not to worry. If your temperature was right and you added water and got the humidity right the rest is down to nature. Enjoy the journey.