What is a blood ring, what does it look like in candling, why does it happen and is there anything that can prevent it?
A blood ring occurs during the incubation of chicken eggs when the chick begins to develop but then dies.
The blood vessels which had begun to form begin to decompose and, rather than remaining attached to the embryo, they float in the yolk and form a circle which spans the circumference of the egg.
It's quite a distinctive sight. When you candle an egg and it's developing normally, what you'll see is a system of blood vessels which spread evenly across the surface of the yolk and look, at least in its early stages, like a spider.
This is a photo of one of my normally developing eggs at day 7 of incubation. You can clearly see how the blood vessels are evenly distributed across the egg in a kind of spider's web radiating out from the embryo at the top of the picture.
When there's a blood ring, rather than this pattern you'll see a dark line running around the circumference of the egg. Below is a photograph of what it looks like when the blood ring has formed at around the same day of incubation - day 7.
This was a bantam egg I was hatching. Note the saddle-shaped air cell - a result of the egg having been sent through the mail. It's not unheard of for an egg with a saddle-shaped cell to survive - I've hatched several - but it's more common for them not to develop past the early stages of incubation, as happened here.
Here you can see the distinctive dark ring towards the top of the picture. If the egg had been left for longer, this would have become thicker as the blood vessels collected.
Underneath you can see a series of dots - these are blood vessels which have disconnected from the embryo and not yet joined the upper ring.
And in the picture below, taken from the opposite side of the egg, it's very easy to see the embryo with the blood ring attached on the right hand side of the image and the disconnected vessels at the bottom.
There's a lot of information on the internet which says that's what it is but actually - no.
The blood ring itself is just that - a ring of blood vessels. Of course, decomposing matter does produce bacteria but that's not what you can see when candling an egg. What you can see is the decomposing circulatory system, as you can see very clearly if you open the egg.
The embryo has died and the blood vessels have separated from it. This is a photo of the same egg from the inside. This chick has died at around day 7.
The dark ring on the left is the blood ring we could see at the top of the picture of the candled egg above. On the left are the spots of blood which formed the broken chain we could see.
The embryo has started to develop but stopped at about day 7.
There could be a number of reasons for this.
This video might be upsetting for some. If you're at all squeamish please don't watch it and also be aware it may upset children. I'm showing it because it's important to know what this is.
The video is of the same egg candled at day 8. It looks at the egg from the outside but I then open it up
and we can see what's happened inside, including the dead embryo. It looks
like it died at around day 7. It's not particularly gruesome as the embryo is still in a very early stage of development.
It's very important to be able to identify eggs like this because, if they were left in the incubator, they would decompose and eventually there's a danger they would explode.
But again this is for instructive purposes particularly for those hatching who have not seen it before : if you think you would be upset, do not watch it!
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If you want to know more about incubation and candling, these pages may interest you. Just click the pic to go to that page.