How to tell if hens eggs are fertilized

Hens do not need a rooster to lay eggs. In fact, almost every egg on the grocery store shelves was laid by a hen that did not have access to a rooster! It just doesn't make financial sense for commercial egg laying flocks to have a rooster since they're usually all caged.

egg yolks of fertilized eggs

However, many homestead flocks, breeding flocks or commercial flocks that sell fertile eggs have roosters! And of course the roosters job is to fertilize said eggs. 

Well, he actually fertilizes the hen and she stores the sperm in storage tubules until she needs it. One egg is produced by a hen per day, so she basically uses the sperm throughout the next few weeks.

When a rooster mates a hen, she can produce fertile eggs for up to 3 weeks later. So if you have a rooster with your hens, how do you know if her eggs are fertile or not? Well unfortunately no matter what anybody says online... and I've read some doozies... you cannot tell if an egg is fertile unless you crack it open, or attempt to incubate it.

When you crack open an egg you will see the germinal disc, also called the blastodisc. It's a light or white spot that sits on top of the yolk. If you don't see it at first, you might have to gently flip your yolk to see the other side. 

By looking at the shape of this disc, you can tell if the egg is fertilized or not. A fertilized blastodisc is called a blastoderm. Here's how to tell if it's fertilized.

How to tell if an egg is fertile 

It's really simple actually, but I will add some pictures to help. Once the egg is fertilized, the blastoderm has a line around it which makes it look more like a bullseye than just a spot.

See in these pictures? That second circle around the disc in the fertilized egg shows you that the egg is actually fertile.

Fertilized and unfertilized egg yolks in dish

I know it's just a tiny difference but the more you look for and recognize the blastoderm, the easier it gets!

How to tell if an incubated egg is fertilized

Now if you decide to incubate this egg instead of breaking it open, after 3 days you should be able to tell either by candling or cracking open the egg. You'll notice small spider-like red lines. These are the beginning of a baby chick.

Of course if you want to hatch a chick you won't want to crack open the egg! Instead use a flashlight to look into the egg and see if the embryo is beginning to form. It should look like a small reddish spider (almost) with the 'legs' going out from a small circle. The lighter colored the eggshell, the easier it is to see when candling!

Here's a picture of an egg that was opened after incubating for a few days.

Egg yolk that's been incubated 3 days

There's no known way to tell if an egg has been fertilized from the outside of the egg. There are different theories, but that's kind of like the theory that round eggs hatch more pullets than pointed eggs, as that's been proven wrong too.

Do blood spots mean an egg is fertilized?

Blood spots near the blastoderm do not indicate fertility. This is totally different. Lots of people believe the saying that a blood spot means a rooster was there. While that can be true in some instances, it can also be caused by many other reasons and it's more likely that a blood spot happened because of something the hen did than by being mated by a rooster. 

Blood spots are caused by a blood vessel in the reproductive tract rupturing. This could be caused by a rooster, but could also be caused by a hen getting a fright or jumping down off a perch wrong.Related reading: Why are there blood spots in my eggs?

To have good fertility in a flock, most chicken keepers like to have 6-8 hens per rooster. Of course this also depends on your rooster. Some roosters have favorite hens they give all their attention too and some roosters manage to service them all.

You'll have to check the eggs from various hens occasionally to see if they are all being fertilized, if not you may need to add an extra rooster to the flock. I always like to have a spare roo anyway! If you are experiencing low fertility then an extra rooster should fix that right up for you! 

Related reading: Tired of finding dirty eggs in the nest boxes? You Here's how to make sure the eggs you collect are clean starting with the hens. 


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