Everything You Need to Know About How a Chicken Lays Eggs

Posted by Daphne Cybele
how chickens lay eggs
Photo: Daphne Cybele

If you have questions about how a chicken lays eggs, we've got answers.

One of the most common questions about keeping backyard chickens is "Do you need a rooster to get eggs from chickens?"

The answer? No, your hens are perfectly capable of laying eggs without a rooster. You do, however, need a rooster if you want baby chicks to hatch from eggs gathered from your backyard hens.

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chicken eggs
Photo: Daphne Cybele

Each egg takes 24-26 hours to form, which is broken down into four main parts below. In addition to how the egg forms, we'll also talk about light, age, calcium, and a popular misconception about finding a chick in an egg. So let's get to the egg-laying questions!

Step One: The Yolk Releases (15 minutes)

Within the developing ovary of each hen are the thousands of potential eggs. Each of these potential eggs is an ovum (or ova if you want to refer to all of them at once).

How A Chicken Produces Eggs
Photo: Cluckin.net

At any rate, when your hen gets towards laying age (about five months in some breeds, longer in others) a few of the ova within a hen's ovary begin to mature into what we recognize as an egg yolk. Each ovum (or yolk) is contained within its own follicle. When a yolk is ready to move to the next stage, it releases from its follicle and travels out of the ovary and down the reproductive tract, also known as the oviduct.

Weird fact: Hens have only one functioning ovary, but they are born with two ovaries. At hatch, one ovary continues to develop in the hen's body, and one simply stops. Why? It is common in birds to have one ovary. This is a sort of streamlining that is likely to help with flight (less bulk and less weight). 

how a chicken lays eggs
Photo: Anatomical Prints

Step Two: The White Forms (four-plus hours)

The yolk leaves the ovary and enters what we call the oviduct by way of the infundibulum, or entrance to the oviduct. This is where the egg would be fertilized if you did have a rooster. You know that tiny whitish spot you see on every egg yolk? That's a single female cell called a blastodisc. If it is fertilized by your rooster's sperm, cell division and embryo development begins and turns the blastodisc into what we call a blastoderm.

chicken egg x-ray
Photo: Cluckin.net

No rooster? No worries. Regardless of whether it is fertilized or not, the yolk (now known as a blastodisc or blastoderm) travels down through the magnum and the isthmus sections of the oviduct. This is where most of the albumen (known as egg white) forms around the yolk, and a thin outer shell membrane holds everything loosely together. Chalazae anchor the yolk roughly in the middle of the egg. At this point, the egg looks more like an egg, but we're still missing the outer shell.

Step Three: The Eggshell (21-plus hours)

The egg formation process continues as the egg gains its shell in the uterus via a shell gland. The shell takes about 20 hours to form and perhaps another hour for the color, or pigment, to be applied to the outer eggshell. This is where the eggshell gets its color, whether blue, white, brown, or green. Finally, the outermost eggshell layer is known as the bloom or cuticle. This outermost layer forms a protective anti-microbial layer on the shell.

How chickens lay eggs
Photo: Penn State Extension

Step Four: The Nest Box

Your hens lay eggs through their cloaca, or what we call the vent. While eggs exit through the same vent used for everything a chicken excretes, the tissue of the uterus extends with the egg (a sort of inside-out trick) until the egg is entirely out of the vent. This little trick along with the bloom layer applied to the shell keeps the egg clean.

About half an hour after a hen lays, the process begins all over again. You don't need one nest box per hen, but you should have, at a minimum, at least one nest box for every four hens.

How Light Changes Egg Laying

Most hens lay more eggs in the spring and summer, and taper production during the fall and winter under natural light conditions. Hens need long days to lay eggs. We give our hens a break during the winter. We don't recommend adding a light to the coop to extend egg production and laying period. If you do wish to add a light, a light bulb should be on a timer and go on in the early morning hours when it's still dark.

anatomy of a chicken
Illustration: Hobby Farms

How Age Changes Egg Laying

Many hens continue to lay past five years of age. If your hens have stopped laying and they are only a few years old, it is more likely that it is either a molt or the season, not their age. Raising chickens is not entirely about egg laying. Do you know how to keep your older chickens from getting creaky and cranky? 

Calcium Supplements

Chicken eggs take a lot of calcium to produce. Chickens with a nutritional deficiency may not lay properly or as much, and you may see a difference in shell quality. If you collect eggs with thinner eggshells it may be that as your hens calcium stores have dropped. Calcium leaches from their bones and other (now depleted) bodily stores. You need to supplement their diet better with free-choice crushed oyster shells or some other calcium source.  

How A Chicken Produces Eggs
Illustration: Extension.org

Finally, Is There a Chick in My Egg?

The only way you would ever crack open an egg and find a chick is if you 1) have a rooster and 2) you don't gather eggs every day (or every other day). You are never, ever, going to crack open a freshly laid egg and find a baby chick.

Even if you have a rooster, it takes three weeks for a chick to hatch from an egg with a warm broody hen on her nest or in an egg incubator. If you are gathering eggs each day, there is no time for any sort of egg development.

In conclusion, that is everything you need to know about how a chicken lays eggs. Now go out and impress your friends with your newfound knowledge!

What's your favorite egg-laying misconception? Let us know in the comments below!

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Everything You Need to Know About How a Chicken Lays Eggs