Why do chickens lay unfertilized eggs?

In nature, a chicken will live its normal life, mate with another chicken, and produce eggs. The egg coming from that chicken is a fertilized egg, and it will develop into a beautiful baby chicken.

However, that is not always the case with farm-raised chickens. The roosters may not be around the coop to fertilize the eggs for multiple reasons. So why do chickens lay unfertilized eggs?

What is an unfertilized egg?

An unfertilized egg only has the hen’s genetic material, which means no chick can come from that egg. On the egg’s yolk, there is a light-colored dot with an irregular border. That is the hen’s genetic material, also known as the blastodisc.

With a fertilized egg, the blastodisc is the blastoderm. It has a bullseye appearance with a regular concentric shape instead of an irregularly-shaped dot. The blastoderm can later develop into a chick.

Why do chickens lay unfertilized eggs?

Regardless of whether the roosters are present or not, the hens can and will still try to lay eggs to collect a clutch of eggs. The eggs laid without the roosters’ involvement are unfertilized eggs.

Fertilized egg vs. unfertilized egg

Fertilized egg vs. unfertilized egg

Normally, the hens will attempt to lay 1 or more eggs every day until they collect their own clutch of eggs. This explains why the hen will keep laying when you remove the eggs every day because that is their goal.

Their goal comes from the fact that chickens are quite near the bottom of the food chain in nature, so threats from predators are prominent.

So they will try to lay lots of eggs and raise a big flock of chickens to make sure there are chickens that could make it to adulthood to continue their life cycle.

The hen doesn’t know if its eggs are fertilized or not, so in the hope that the eggs will be fertilized, it lays more eggs. This only works well if a rooster is present around and the hen mates with the rooster.

Related: Can a chicken lay 2 eggs a day?

Do chickens lay unfertilized eggs naturally?

A healthy female chicken can and will lay eggs regardless if the male chicken is present or not. If there is no rooster involved during the formation of the egg. The egg will be unfertilized, which means it can not become a chick.

How often do chickens lay unfertilized eggs?

A female will usually lay eggs (fertilized or unfertilized) about once a day. This is because the formation of the egg takes up more than 1 day, with more than 4 hours to form the inside, and more than 20 hours to form the eggshell.

However, there may be a chance that a chicken can lay 2 eggs a day though it is rare. This happens more often on maturing chickens or chickens that have been overfed.

With the case of 2 eggs a day, the shell where 2 eggs contact each other will be poorly calcified, and both eggs will show flat sides. This results in more dehydration while incubating due to poor shell quality.

However, chickens don’t always lay 1 egg per day, everyday. There are many factors that can make the chickens skip laying for a few days or stop laying for a long time. They include: weather, lighting, the molting process, or poor health condition.

Unfertilized eggs look identical to fertilized eggs on the outside
Unfertilized eggs look identical to fertilized eggs on the outside – Image credit by Kirsty

Are the eggs we eat fertilized eggs?

If you buy the eggs from a store, there is a high chance that those eggs were not fertilized. Apart from the tiny irregularly-shaped white dot on the yolk, there is no way to tell if the eggs are unfertilized or fertilized.

As mentioned, even the chickens don’t know if their eggs are fertilized. They just simply lay their eggs. This behavior also occurs with other female birds, just at a far lower rate.

However, there are some factors that make people believe that the egg is fertilized, while in fact, those are not the indicators:

  • Red spots:

They are just broken blood vessels and it doesn’t indicate that the egg is fertilized.

  • White strings:

People mistake this as an umbilical cord. But, it is called a chalaza. Its main function is to keep the yolk suspended to prevent it from smashing into the shell.

This is more prominent in farm eggs because the chalaza dissolves as the egg ages. And store-bought eggs are aged longer than farm ones.

Why do chickens sit on unfertilized eggs?

After laying enough eggs to make a clutch of eggs, the hen will sit on the eggs, so why does it happen?

The hens are just driven by their instinct of reproducing by keeping the eggs warm. As with most birds, the hen can’t know the eggs in its nest are fertile or not and will just sit on them and incubate.

But, after about 10 to 14 days, the hens can sense if something is off about the eggs. As a result, it may leave the nest if it feels something is wrong.


So, Why do chickens lay unfertilized eggs? It is just their instinct to lay many eggs regardless of whether a rooster is present or not. The roosters are not necessary for the production of eggs in the hens.

This instinct is a response to the fact that chickens can be easily hunted down by many predators in nature, so they will try to lay lots of eggs and raise them so that there will be some that could survive.

The hens have no way to know if the eggs are fertilized or not, so they will keep laying and stop when there is a clutch of eggs. But, after incubating for about 10 to 14 days, they can tell something is off and thus, decide to leave the nest.