As far as eating goes, fertile eggs are no different than unfertile eggs, nutritionally or taste-wise or otherwise.
Fertile eggs Are different in that they have the Potential to develop into chicks, ONLY if they are incubated for 20-21 days at critical temperatures and humidity levels. During incubation the fertilized blastoderm (a tiny white speck on the outside of the yolk) divides into multiple cells to form the developing chick. The yolk itself is only the food source for the growing chick - it never becomes the chick. All egg yolks, whether from fertile or unfertile eggs, have a blastoderm speck. But a fertile blastoderm will have a white ring around it, like a bullseye.
They can get pretty creepy if they are kept too long- anyone remember the red bloody egg that was in another post?
There are not many things as gross as cracking a fresh egg into a frying pan and having a partially formed chick fall out.
All it means is that there is at least one rooster running with the flock of hens and you could incubate the eggs and get chicks if you wanted.
I have raised chickens for years and not all eggs are fertile. They are only fertile if you have roosters with the hens. But all that means is there is a developing embryo on the side of the yolk; you can see it. So of course you want to keep the eggs refrigerated so the embryo does not begin to grow, though in some cultures these are considered a delicacy! I doubt they are any more nutritious simply because of the fertilization.
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