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How Exactly do Chickens Lay Eggs?

Chickens lay eggs by receiving light cues.
A chick and an egg.
A chicken egg.
Brown and white chicken eggs.
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  • Written By: Michael Pollick
  • Edited By: Bronwyn Harris
  • Last Modified Date: 17 August 2014
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Believe it or not, the egg laying process for a chicken begins in its eye. Chickens lay eggs only after receiving a light cue, either from natural sunlight entering a coop or artificial light illuminating a commercial egg hatchery. The light stimulates a photo-receptive gland near the chicken's eye, which in turn triggers the release of an egg cell from the chicken's ovary.

Most chickens lay eggs on an almost daily basis, unlike some other egg-laying animals which only release an egg every thirty days or so. The chicken also releases a small disk of material which surrounds the egg cell and provides nutrition. The chicken's uterus also fills up with albumen, the viscous substance we know better as egg white.

Meanwhile, a membrane forms around the inside uterine wall, which seals in the egg cell, yolk and albumen. Eventually a mixture of water, salt and calcium surround this membrane and form a thin but structurally sturdy outer shell. This shell is molded in the shape of the uterine wall, thus giving a chicken's egg its distinctive shape. While in the uterus, the egg's narrower end points downward, but it will later turn and be ejected wider end first.

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Once the egg has fully formed, the chicken's uterus begins to contract in an effort to expel it. The egg moves down a vaginal canal towards an external opening known as a vent. The vent is a common opening for both egg laying and waste elimination, but a chicken cannot perform both functions at the same time. An internal flap known as a cloaca keeps the vaginal canal and the intestinal track separate until either an egg or excrement reach the vent. When a chicken is laying an egg, the cloaca descends and blocks the intestinal track.

Once the egg passes the cloaca, it is carefully expelled through a series of muscular contractions which essentially turn the vaginal canal and cloaca inside out at one point. Eventually the egg is pushed out through the vent and ideally lands intact on the ground. Many chickens let out an audible cluck at this point, but designated egg layers rarely display any other maternal concern. These chickens lay eggs every 24 to 36 hours at the height of their productive years, so individual eggs rarely attract their attention.

Once a chicken lays a certain number of eggs, it may stop producing more eggs and go into a "brooding" stage, a maternal stage in which the mother will sit on her eggs until they hatch. In order to prevent egg layers from brooding, freshly laid eggs must be removed on a daily basis. Chickens lay eggs as long as they believe they need more to form a proper brood. The egg laying process continues whether or not a rooster provides enough sperm for fertilization. A chicken cannot tell if an individual egg has been successfully fertilized or not.

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Discuss this Article

anon954296
Post 49

Thanks for the concise article. Very informative.

anon924829
Post 48

I forgot how much light chickens need to lay eggs. Also, usually after 11 or 12, months they will stop laying during molting, when they grow all new feathers, and it usually takes about a month for them to start laying again. After molting they will produce larger eggs, but maybe not every day.

anon349860
Post 47

It is really great to read this blog for it has complete ideas and techniques as well as giving helpful images that helped me understand the whole idea of hatching eggs. I wonder if they can give idea also on how to make an incubator. Thanks!

anon328183
Post 45

One of my chickens was away from the nest and I notice that she was running toward the nest with her back end kind of in a swat, and out came an egg. She was still running, trying to make it to her nest. So funny

anon322655
Post 44

Not so yummy when you actually take the time to think about the origin of the egg - from a chicken's uterus. No thanks!

bluedolphin
Post 43

@anon49031-- I have seen chickens lay eggs closely many times. Not that I enjoy watching them do that, but I have to help my dad with raising chickens at the farm.

Anyway, I don't think it's painful. I don't meant to gross anyone out here, but the way they act while laying the egg is similar to a bowel movement. Just some exertion, the opening expands and whoop, the egg pops out. It's really easier and faster than what people think.

I know some hens make a lot of noise while doing it, but it's not from pain. If the chicken is acting like she's in pain while laying eggs, there might be something else going on.

burcidi
Post 42

@anon284874-- I'm not an expert on this but I thought that they can start laying eggs before six months.

How are you keeping your chickens? Are they seeing sunlight? Don't forget they need to see light to lay eggs.

Also, don't be surprised if they just lay one egg per day and if the eggs are very small at first. Younger chickens tend to lay smaller eggs and the eggs will get larger over time. Older chickens will produce less eggs and might even stop laying eggs after a certain age.

They also tend to lay less eggs in winter since the day is shorter and they won't get as much light.

fify
Post 41

I feel like chickens are being cheated by humans. They go through so much to lay eggs every day and then we just take it and eat it.

Does laying eggs hurt them? It must right? It's like they're giving birth every day. I wonder why they lay eggs so often when other animals don't.

anon284979
Post 39

I have a chicken that is losing weight. I purchased her six weeks ago. I have wormed her but I think it's too late. Her crop seems empty all the time. Any ideas, please? The other three girls are fine. --Bob

anon284874
Post 38

I have six chickens I bought. I just read they start laying at six months old, and they are almost there. What is my next step to start getting some eggs? Help a poor Oklahoma girl out!

anon283287
Post 37

No, a rooster is not needed for an egg to be laid. A chicken will lay eggs regardless. The only reason a rooster would be needed is if one wanted to hatch the eggs (either through a brooding chicken, or an incubator).

anon278205
Post 36

Do chickens act different when it's time to start to lay eggs? Do they go off and sit away from the others? --Bob

Mixalis
Post 35

very interesting stuff. But does anyone know why chicken lay eggs at all?(except for reproductive reasons).

anon158644
Post 32

thank you very much, you helped me in my project.

anon157622
Post 31

Since there is no umbilical, how do the embryos oxygenate? If they breathe, are they breathing air or liquid? Great article, thanks.

anon138082
Post 28

Very informative. Thanks.

anon137463
Post 27

Can you please advise if chickens have a uterus?

This article says they do, but others I have read say they don't. Thanks.

anon105482
Post 25

My husband told me an egg comes out of the same opening as the feces. I told him no way! I was very surprised and grossed out to learn he was correct. Thanks for the info and ending our argument on this subject.

anon87319
Post 24

wow. this was educational and informative enough! thanks so much.

anon63195
Post 18

what great info. thanks.

anon58966
Post 17

Thanks for the info. you helped me with my science fair project!

anon55383
Post 16

Its very informative. I learned something new today about the egg-laying process. it was for our science class. The kids had so many questions about all of this and this article had all the answers thank you.

anon49031
Post 13

My chickens just laid there first egg, it sounded very painfull...is it? Even saw some blood on the shell... Great article about the egg cycle and how to keep them laying

anon48514
Post 12

it's great! :) Thumbs up!

anon44274
Post 10

I had two debates over the "chicken vs the egg". Through this article I was able to get both answers.

anon43217
Post 9

good information. i was really curious!

anon42047
Post 8

Thanks for the information. regards --keith

anon40107
Post 7

Very imformative. Thank you

anon16616
Post 5

this is a very interesting article. i want to know further that how do chickens give birth to their child, i mean what is the process of brooding?

anon16231
Post 3

could a chicken that has never come in contact with a rooster still lay eggs? and is it pleasure or pain? why do they let out a distinct sound?

anon16111
Post 2

Very informative, have been around chickens for years and had no knowledge of the cycle. Thank you for sharing.

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