How Does a Chicken Make an Egg Shell? (PROCESS)

How does a chicken produce an egg?
Chicken eggs are one of the most nutritious foods available. They’re a great source of vitamin D and other vitamins and reduce the risk of heart disease. But how does a chicken make an egg? Simply put, it starts with the yolk production in the hen’s ovary. The yolk is either left unfertilized or fertilized by a rooster, then moves through a process of adding the other egg components until it’s ready to be laid.  The interest in egg production has begged the centuries-old question, “What came first, the chicken or the egg?” The answer lies in the process of producing the egg.

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How Do Chickens Produce an Egg?

baby chick in an egg
The way chickens produce eggs is extremely fascinating and a lot of people find it to be a mystery.
  Hens can lay eggs with or without roosters. But, to fertilize the egg, the rooster is a necessity.  Hens begin working on the egg before fertilization can even begin. Once the egg yolk is formed it moves down allowing a rooster to fertilize it. Once the egg is fertilized, that’s when it moves on to creating the egg white.  Lastly, the hen works on creating the shell which takes the longest time out of all the egg components. However, when the shell is done, that’s when she’s ready to lay her eggs. It’s important to note that even without fertilization, these same steps will still happen, but the eggs that the hen lays will be unfertilized and unable to hatch into a chick. 


The rooster’s cloaca has a bump called a “papilla” inside it where the sperm is released. The hen extends her cloaca to help the sperm reach the egg. The sperm collected in the hen’s cloaca will fertilize the waiting egg. Excess sperm is collected in sperm pockets and can be used to fertilize other eggs for up to 5 days.  The following video shows several parts of the egg that are produced after fertilization: 


What Are the Parts of an Egg?

The egg is much more than the white, the shell, and the yolk:
  • The yolk is the yellow center part of the egg. It’s the first of the egg’s elements to be formed.
  • The albumen is the clear part near the yolk. We call it the egg’s white because of the color it turns when cooked. There are two layers of albumen, one thin and one thick.
  •  The chalaza is tightly twisted albumen that functions to keep the yolk from sticking to the shell. It also keeps it centered.
  • The shell membranes are two mucous layers of membranes that encase the egg parts.
  • The shell is the outer protective layer made mostly of calcium carbonate (CaCO3) crystals.

Laying the Egg

How does a chicken lay an egg? The chicken produces her egg inside of the reproductive tract’s ovary. The yolk is formed in the ovary and is eventually released through ovulation. It then goes through a funnel-like tube called the infundibulum, where fertilization happens. The egg is soon ready to be laid. It gets pushed out through the hen’s vent, which is near the cloaca, with the large end emerging first. Since chicken pee and feces also pass through this way, the large-end-first process keeps fecal contaminants away during egg laying.

Are the Eggs We Eat Fertilized?

Probably not. First of all, many farmers who produce eggs for the market don’t even have roosters on their farms. A hen will lay an egg regardless of whether or not a rooster is present. Even if a rooster fertilizes an egg meant for eating, the egg will not automatically produce a baby chick. There are ways to prevent a fertilized egg from forming an embryo.
  • Farmers gather eggs daily, which prevents hens from becoming broody (wishing or inclined to incubate eggs).
  • The eggs are refrigerated at between 32 and 40 degrees Fahrenheit.
  • Eggs that get to the grocery store have not had the time nor the right conditions to develop a chick.
Read our related article, Do Chickens Produce Eggs Without a Rooster? to learn more!

How Do Chickens Lay Eggs Without Mating?

Hens don’t need roosters to lay eggs. Roosters are typically only introduced to a flock of hens when a farmer desires the hens to become broody.  Just like humans, hens are born with a predetermined number of eggs in their ovaries. The eggs are released regardless of being fertilized. Birds are unique, however, in how their eggs develop.
  • Hens can begin to lay eggs by 18 weeks old. 
  • The hen will continue to lay eggs for about four years of its 6-8 year lifespan, that’s a lot of egg-laying
  • It takes about 26 hours for an egg to form fully. 
Some studies say that hens can lay an egg every day, but the 26-hour time frame makes it a little less than that. Still, that’s a hefty amount of egg production.

Do Chickens Know if Their Eggs are Fertilized?

Even though a rooster may mate with a hen, he may be infertile. The hen won’t know this. When she lays an egg, she has no idea whether or not it’s a fertilized one. There are newer breeds of hens that have had their natural brooding instincts bred right out of them. They will lay their eggs and then walk away. This is often done to commercially bred hens to ensure their eggs don’t get incubated. Read our related article, How is a Chicken Egg Fertilized? This educational guide covers the reproductive process of chickens!

Why Do Chickens Eat Their Own Eggs?

Chickens are omnivores and in the wild, they do eat their own eggs. However, even domesticated hens may resort to eating their own eggs if they aren’t getting enough nutrition from their feed. Other reasons  may include:
  • Overcrowded coops
  • Not enough nesting boxes
  • Boredom

Once an Egg is Laid How Long Until it Hatches?

eggs in a carton
Keeping the conditions pristine and giving your chickens the proper nutrition and security is key to having your hen lay regular eggs. 
When hens sit on their eggs, they hatch in 20 to 21 days. Hens keep them at the correct temperature naturally. They instinctively know to keep the humidity between 60% and 80% by splashing water from their beaks onto the eggs.

Incubating a Chicken Egg

Eggs can hatch in incubators as well. Temperature is critical with this form of incubation. It should remain between 100 and 102°F, or the embryo could be lost.  It takes 21 days for an incubated egg to hatch as well. There are some crucial things to remember when hatching eggs in an incubator:
  • You can’t hatch dirty eggs. However, you can wash off eggs that are only slightly soiled
  • You should store eggs with the small ends pointing downward to keep bacteria away from the yolks.
  • You can’t store fertilized eggs for more than 7 days before incubating, so be sure to move quickly after they are laid
Read our related article on How to Candle a Chicken Egg With a Flashlight. You’ll need to candle to check for life, and here’s how you do it!

How to Build an Incubator

Before building an incubator, you need some essential components. Remember that your container should be well insulated, so the humidity and temperature remain constant. Some containers people have had success with are:
  • Empty cleaned-out fish tanks
  • Cardboard boxes 
  • Styrofoam containers
  • Picnic coolers
You also need a heat source, such as a chick warmer plate. People have had luck with 25-watt bulbs, which they’ve attached to lamp fittings and electric heating pads.  Adding little stones to the bottom of the container can help to retain heat. Keep the heating element away from the eggs to prevent burning. Strong wire mesh works well.  However you decide to build an incubator, you’ll be put in the position of a broody hen. It’ll be your job to maintain the heat and humidity for the hatching eggs. Here is a video that shows you how to build an incubator with a cardboard box:

Increasing Egg Production in Chickens

Whether producing table eggs for eating or hatching eggs for breeders, nutrition is an essential factor of production.


Hens don’t eat much daily because of their smaller size, so their feed should be nutrient dense. Once they become layers, there are several things to consider:
  • The feed should be rich in antioxidants, like magnesium and betaine, to boost their immune systems.
  • Chickens need calcium conjointly with vitamin D and phosphorus, as found in crushed oyster shells.
  • The feed should have a protein source, such as mealworms, insects, or chick starters.
  • Amino acids, vitamins, and mineral help in producing wholesome eggs.
  • Feed needs to be stored in airtight containers to keep out parasites.


In addition to proper nutrition, hens need clean nests. Keeping nests clean and comfortable with soft bedding promotes healthy hens who lay healthy eggs. Keeping their coops safe and secure from predators is also essential. Other important considerations for promoting increased egg production are ensuring the hens have an open area to graze on grass and changing their water daily to maintain their health. A small heated chicken waterer is great to have during the winter months to keep it at an ideal temperature.


Hopefully, this article helped you to understand how exactly a chicken makes an egg and what happens to make it a chick versus an edible egg.

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