How is Chicken Egg Fertilized – The BASICS

How is a chicken egg fertilized by a rooster?
Most people who eat chicken eggs likely assume that the eggs have been fertilized through a natural process. This incorrect assumption may prevent some people from eating eggs or may cause people raising chickens to incubate the wrong eggs. So how are chicken eggs fertilized by a rooster? Chicken eggs are fertilized by copulation between a hen and a rooster. However, hens can lay unfertilized eggs without the need for a rooster. Because most commercial hens are raised without roosters, most chicken eggs are unfertilized. Read on to learn more about the differences between fertilized and unfertilized eggs and what this means for both eating chicken eggs and raising chickens.

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How are Chicken Eggs Fertilized Naturally?

how are eggs fertilized
Believe it or not, egg fertilization when it comes to chickens is something that a lot of people don’t know about or understand. That’s why we wanted to help clear up some information!
Chicken eggs are fertilized through the natural process of mating or copulation between a female hen and a male rooster. After copulation, a hen can lay up to 10 fertilized eggs Eggs are fertilized when the yolk is created within the hen’s body. As the yolk enters the first part of the oviduct, fertilization takes place if the hen has recently mated with a rooster. It’s important to note that hens are able to lay eggs without the need for fertilization. Even if a hen has not mated with a rooster, she will still continue to lay eggs. The only difference is that the eggs will not be fertilized. Read our related article, How Do Chickens Lay Eggs Without a Rooster? for more on unfertilized eggs!

Is an Unfertilized Egg Alive?

Unfertilized chicken eggs are not alive. Only fertilized eggs have the potential to grow into a baby chicken, and this process only occurs if an egg is properly incubated. Without incubation, nothing living will develop within a chicken egg and essentially it would be the same as an unfertilized egg. This may make many consumers feel better about eating eggs since the eggs do not contain a baby chicken. This may be concerning to new chicken hobbyists, though, as they may not know that only fertilized eggs can be incubated and can hatch a new chicken. Read our related article, Why Do Chickens Lay Unfertilized Eggs? where we cover the science (and selective breeding) behind unfertilized chicken eggs!

How Can You Tell if a Chicken Egg is Fertilized?

The germinal disc is something that you probably have never seen in person because the eggs we buy in the store aren’t fertilized.
To determine if a chicken egg is fertilized, you can crack the egg open and look at the yolk. If the egg has been fertilized, you will see a small white spot that is about 4mm in diameter.  The spot is called the germinal disc. The disc only appears if the egg has been fertilized. Keep a few things in mind:
  • You don’t have to crack open every egg to check for fertilization. If you crack open one egg from a specific hen and see a germinal disc, the hen is likely laying multiple fertilized eggs.
  • If you want to determine if an egg is fertile without breaking it, you will need to incubate the egg and then use a flashlight to candle the egg after around 5-10 days in the incubator. 
WARNING: If you break open the egg, there is no chance of the developing chick surviving. So, if you’re planning to grow your flock, it’s best to candle to check for life. Learn How to Candle a Chicken Egg With a Flashlight in this guide. Read our related article, How Does a Chicken Produce an Egg? Discover the process of egg-making in this guide!

Can Unfertilized Eggs Hatch?

Unfertilized chicken eggs will not hatch. Most eggs purchased in the store are not fertilized. Even if you placed them in an incubator or under a broody hen, they would never hatch. Likewise, eggs left too long in the refrigerator or left out on the counter will not hatch. The eggs would need to be fertilized and then would need to be kept in a warm environment for multiple days in order to hatch a baby chicken. This can present challenges for people who want to raise baby chickens at home.  Here are a few guidelines to follow when it comes to chicken eggs:
  • Do not attempt to incubate store-bought eggs. They are not fertilized, and will not hatch.
  • If you plan to incubate eggs at home, purchase fertilized and properly-stored eggs and use an egg incubator in order for them to hatch.
  • Even if you place a store-bought egg under a broody hen, it will not hatch because it is unfertilized.
Read our related article, How Does a Chicken Lay an Egg? Learn all about egg-making in this guide!

Are the Eggs We Eat Fertilized?

eggs in a bowl for baking
You can technically eat fertilized eggs as they are the same as unfertilized eggs since they’ve not been incubated.
Most commercial hens are not raised in the presence of roosters. For that reason, most eggs bought in the store are not fertilized. That may come as a relief to many consumers of eggs, who worry that their egg might contain a baby chicken or the products of fertilization. Again, for most store-bought eggs, this is not the case. Hens can lay eggs without the need for fertilization. There are some exceptions:
  • Eggs purchased from a local farm are more likely to be fertilized because many hens on small farms are raised with roosters present.
  • If you raise chickens at home and keep both roosters and hens, your eggs are likely to be fertilized.

Is the White Stuff in Chicken Eggs Sperm?

If you’ve cracked open a raw chicken egg, you might have seen a white, stringy substance inside. Some people worry that this substance is a chicken embryo, sperm, or the product of fertilization The white material inside a chicken egg is called a chalaza. It does not result from fertilization and is not part of the chicken embryo. The chalaza is a protein-based structure that helps to hold the yolk to the wall of the egg, keeping it intact. Here are a few things to remember:
  • The chalaza is not an embryo, umbilical cord, or other product of fertilization.
  • Both unfertilized and fertilized eggs have chalazas.
  • The chalaza is harmless and safe to eat.

Are Fertilized Eggs Healthier?

Fertilized eggs are not healthier than unfertilized ones.  The fertilization process adds a relatively negligible number of additional cells to a chicken egg. For that reason, fertilization has little to no effect on an egg’s nutritional value.

How Does an Egg Become a Chicken?

Fertilized eggs become chickens when they are incubated and hatch. Fertilized eggs can be incubated by a mother hen, or by using an egg incubator. During the incubation process, an embryo will develop within a fertilized egg. After 21 days of growth and incubation, the embryo will grow into a chick. The chick will then use its beak to break the shell of the egg and emerge. If the chick is fed after hatching and cared for, it will grow into a chicken. Here’s a video showing the egg incubation and hatching process.

Read our related article on What to Feed Baby Chickens After Hatching to make sure your new chicks grow as they should!


Chicken eggs are fertilized through the natural process of mating and copulation between a female hen and a male rooster. The eggs you buy in the store aren’t fertilized, but you can buy and incubate fertilized eggs if you want to raise chickens. Fertilized eggs must be incubated under specific conditions in order for them to grow into baby chicks.

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