Eggs are one of the most versatile foods around. They can be the main ingredient (like in an omelette or quiche) or the extra in a dish (like in pad thai or spaghetti carbonara). They can also be the unsung hero who makes a cake rise or a soufflé fluffy.
Though they are ubiquitous in the culinary world, the process of how an egg forms inside a hen is not widely understood.
An egg develops through multiple stages during its time inside a hen. A yolk is surrounded by egg white and protective membranes, sealed inside a shell, and covered with a protective fluid that dries quickly.
There are a lot of questions about how eggs are made inside hens. This page will help you find the answers.
One of the healthiest and most useful foods in nature is the egg. But even though eggs are very popular, a lot of people are curious about where they come from and how they are made. This article tells you everything you need to know about eggs and how chickens lay them.
Egg Anatomy
Before diving into egg laying, it’s helpful to understand the basic anatomy of a chicken egg. An egg contains the following key parts:
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Shell: This tough, porous covering keeps germs and damage from getting into the egg. It’s made in the hen’s oviduct just before the egg is laid.
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Inner and outer membranes – These thin membranes line the inside of the shell to protect and cushion the egg
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Air cell: As the egg cools after being laid, an air pocket forms at the round end of it. This allows the contents to expand and contract.
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Chalazae – Rope-like strands of egg white that anchor the yolk in the center of the egg
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This is the protein-rich, clear or cloudy liquid that surrounds the yolk. It is also known as “egg white.” It provides nutrition and protection.
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Yolk – The yellow, nutrient-dense center of the egg where the embryo develops into a chick (if fertilized). It is a major source of vitamins, minerals, fat and protein.
Egg Formation and Laying
Chicken eggs begin their journey in the hen’s ovary. When a yolk matures, it is released into the oviduct, where egg components are added in sequence until the whole egg is formed. The main steps of egg production are:
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Yolk formation – The yolk develops in the ovary in a process called ovulation, taking around 25 hours to mature. Once released, the yolk travels to the oviduct.
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Albumen layers added – In the oviduct, layers of thin albumen are deposited around the yolk over approximately 3 hours. Thick albumen is added last.
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Shell membranes applied – Two shell membranes are formed around the egg contents in the isthmus region of the oviduct. These take around 1.5 hours to complete.
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Shell formation – The egg moves to the uterus where the shell is gradually deposited, taking around 20 hours. Calcium carbonate forms the shell’s crystalline structure.
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Pigment application – Colored breeds add pigment to the shell as the last step, creating brown or blue eggs rather than white.
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Laying – Muscular contractions push the egg out through the vagina/vent. This process takes just seconds.
How Often Do Hens Lay Eggs?
Laying frequency depends on factors like breed, diet, age and season. Most hens ovulate about once per day, so they cannot lay more than this. Breeds developed for commercial egg production tend to lay very regularly, producing 5-6 eggs per week. Heritage breeds may only lay 1-2 times per week.
As chickens age, their laying slows down. They experience natural declines in hormone levels and oviduct function over time. Molting, cold weather and stress can also temporarily stop egg production.
Free-range, well-fed hens with adequate space typically have the best laying rates. Clean nest boxes encourage hens to lay in the right spot.
Can You Eat Eggs From Backyard Chickens?
Absolutely! In fact, eggs from backyard flocks are often superior in flavor and nutrition compared to store-bought. The “bloom” coating on very fresh eggs helps protect their quality. As long as you provide hens with proper feed and housing, their eggs are perfectly safe to eat.
The color of the shell has no effect on nutritional content. However, local eggs tend to be richer with brighter orange yolks due to natural foraging. Store-bought eggs often come from caged hens fed unnatural diets.
As always, proper handling and cooking is important for safety when eating any eggs. But the notion that eggs from family flocks are unsafe is simply a myth. The chickens, eggs and humans all benefit when small backyard flocks are raised responsibly.
How Is an Egg Formed?
A laying hen’s ovary holds thousands of tiny ova, or future egg yolks. Birds are unique among animals because only one ovary (the left) matures to the stage where it releases eggs.
When a yolk is ready, it moves out of the ovary and into the oviduct – a tube-like structure that is divided into different sections. Over four hours, the yolk moves through an area of the oviduct called the magnum where egg white protein is added to it.
There are many different proteins that make up the egg white. The different layers of proteins protect the yolk and make a pattern for how the shell membrane and shell will grow.
The egg quickly goes through a part called the isthmus, where shell membrane fibers are made. Then it goes into the shell gland, where the shell forms over the course of about 20 hours. The process is called calcification as layers of calcium carbonate are added to form the shell.
During the last two hours of shell formation the bulk of the pigment (white or brown) is produced and deposited into the outer layers of the shell. This includes the cuticle, which is put down to protect the shell against bacteria that might try to get through it and the egg’s contents losing water.
The egg then rotates just before laying to be laid large end first, having moved through the oviduct small end first.
Learn More About Egg Production in Australia
Eggs are produced using different methods with the three most common being free range, barn-laid, and cage. While each system has its advantages and disadvantages, the nutritional profile of the eggs is consistent across all systems.
Learn more about these different farming systems today or take Australian Eggs interactive tour of three commercial egg farms.
What Came First The Chicken or The Egg? | The Most Confusing Question | The Dr. Binocs Show
FAQ
Which hole does a chicken egg come out of?
The same part of the chicken makes eggs and poop. That may sound gross. Think of it like a plumbing system: two ‘pipes’ come together in one outlet, in this case the chicken’s cloaca. In humans, we call this the anus (the bumhole).
How does a rooster fertilize the egg?
By touching the hen’s cloaca with its own, the rooster’s cloaca (the opening for the reproductive tract) fertilizes the egg laid by the hen. This is called the “cloacal kiss.”
Where on a chicken does the egg come from?
A laying hen’s ovary holds thousands of tiny ova, or future egg yolks. Birds are unique among animals because only one ovary (the left) matures to the stage where it releases eggs. When the yolk is ready, it leaves the ovary and goes into the oviduct, which is a tube-like structure with different sections.
Do chickens have only one hole?
Understanding the Cloaca:
Unlike humans and most mammals, a female chicken has but one rear orifice with three functions. It is where feces and eggs exit her body and sperm enter. The rooster’s cloaca has only two functions. One is to pass feces.