Interesting Facts About Chicken Eggs

Eggs are amazing things. We often take them for granted, but you won't after you read this article!
By Mrs. Mucket · Feb 22, 2012 · Updated Mar 27, 2012 · ·
  1. Mrs. Mucket
    Have you ever wondered how a hen can lay an egg every day? Why some eggs are brown and some eggs are white? How many days an egg takes to hatch?

    Here are the answers to those questions and many more.

    Hens and eggs
    • Female chickens are called pullets for their first year or until they begin to lay eggs. For most breeds, around 20 weeks is a typical age for the first egg.
    • Some breeds lay eggs daily, some every other day, some once or twice a week.
    • Some individual hens never lay eggs, due to narrow pelvises or other anomalies.
    • Normal laying routines can be interrupted by molting, winter daylight shortage, temperature extremes, illness, poor nutrition, stress, or lack of fresh water. Hens usually return to normal laying habits when the disruption-causing factor ends or is corrected.
    • Most hens are productive layers for two years before declining in production, but some continue to lay eggs for several years.
    • Hens will lay eggs whether or not they’ve ever seen a rooster. Roosters are necessary only for fertilization of eggs.


    Egg development and laying process
    • A female chick is born with thousands of tiny ova, which are undeveloped yolks. Once she reaches maturity, an ovum will be released into a canal called the oviduct and begin its journey of development.
    • At any given time a productive hen will have eggs of several stages within her reproductive system. The eggs most recently discharged from the ovary are just tiny yolks, and the eggs farther down the oviduct are progressively larger and more developed.
    • From the time an ovum leaves the ovary, it takes approximately 25 hours for the egg to reach the vent for laying. During that time period, the yolk will grow larger while being surrounded by albumen (egg white), wrapped in a membrane, and encased in a shell. Pigment is deposited on the shell as the last step of the egg production process.
    • If sperm is present, the yolk will be fertilized before the albumen is deposited.
    • As a chick embryo develops in a fertilized egg, the yolk provides nourishment and the albumen cushions the embryo.
    • Although a hen has only one exterior opening (the cloaca or vent) for egg laying and elimination, eggs are not contaminated during the laying process. Two separate channels, the oviduct and the large intestine, open into the cloaca. As the egg nears the end of the oviduct, the intestinal opening is temporarily blocked off. The egg passes through the cloaca without contact with waste matter.
    • The typical interval between eggs laid is about 25 hours, so a hen that lays an egg every day will lay a bit later each day.
    • Hens don’t usually lay eggs in the dark, so once a hen’s laying cycle reaches dusk time, she will usually not lay till the following morning.
    • Eggshell production drains calcium from the hen’s body. The comb, wattles, legs, and ear lobes will fade as the calcium leaches out. Calcium must be replenished through either feed containing calcium, supplements such as oyster shell, or high amounts of calcium in the soil of birds with outdoor access.


    Egg variations
    • Young pullets often lay malformed eggs before getting established in a normal laying routine. Older hens may occasionally lay abnormal eggs due to age, stress, or illness.
    • Pullet eggs--the first ones produced by each pullet--are smaller than the eggs that the same hen will produce as an older hen.
    • “Fart egg” and “oops egg” are terms for tiny eggs that quickly pass through the oviduct without reaching full size.
    • Shell-less eggs are released before they have time to develop a shell. They may have membrane holding them together or just be loose yolk and white.
    • Double eggs or “egg in an egg” are created when an egg with a shell is encased by the next egg in the oviduct and a shell is produced over the outer egg as well.
    • Double yolkers may have a normal amount of egg white with two or more yolks. In the shell, the egg may be unusually large.
    • Yolkless eggs, also called no-yolkers, dwarf eggs or wind eggs, consist of egg white alone.
    • Occasionally an egg will come out with a wrinkly, misshapen, rough, bumpy, or unusually colored shell.
    • Egg size is dependent on breed, age, and weight of the hen. Larger chicken breeds tend to lay larger eggs; banty breeds lay small eggs. Older hens tend to lay larger eggs than younger hens.
    • The shell color is a breed characteristic. Most chicken breeds lay light-to-medium brown eggs. A few breeds lay white, dark brown, green, blue, or cream colored eggs.
    • Shell color is only “skin deep”-- the eggs inside are the same as eggs of other colors.
    • The shell color intensity of eggs laid by one hen can vary from time to time, with an occasional darker or lighter eggshell.
    • While most eggs have a slight sheen to the shell, some breeds or individual hens tend to lay eggs with a chalkier texture.


    Chicken-and-egg behavior
    • Most hens will lay eggs in the same nest box as flockmates, so it’s not necessary to have a nest box for each hen.
    • Some hens like to lay their eggs in private and others will join their sisters in the nest box. Often two or three hens will crowd into one box while another nest box remains empty.
    • Sometimes a hen will sit on previously laid eggs and add her egg to the clutch. Another might prefer to sit in another area and deposit one egg by itself.
    • Often a hen will sing “the egg song” before or after she lays an egg. Some will sing during the process of laying. It is a cheerful song that seems to be a proud announcement.
    • Chickens learn by example, so a fake or real egg left in a designated nest box may encourage hens to lay there instead of on the floor or outdoors.
    • Unconfined hens may lay eggs anywhere outdoors if they don’t want to return to the nest box. Sometimes a free-ranging hen will go missing and reappear weeks later with a parade of chicks.
    • Chickens like to eat eggs, even their own. An egg that gets accidentally broken will likely be eaten by one of the chickens. If you occasionally find pieces of shell or egg yolk in the nest box, it’s usually nothing to be concerned about.
    • Some chickens become habitual egg-eaters that break eggs open and eat them. An egg-eater should be culled from the flock if you wish to have eggs for the kitchen. Not only will that chicken continue to eat eggs, but others will learn from watching and you may end up with several egg-eaters.
    • Holes in eggs and cracked eggs do not necessarily mean there is an egg-eater in the flock. A hen can accidentally crack an egg in the nest when she sits down or adjusts the nest to lay her own egg. Sometimes curiosity or boredom leads a chicken to peck at an egg without the intention of eating it.
    • Chickens can be fed their own or other eggs either raw or cooked. Eggs provide protein and the calcium in the shell is beneficial for laying hens. A potato masher can be used to break boiled eggs into pieces of egg and shell.
    • Empty eggshells from the kitchen can be fed back to chickens as a calcium supplement without concern for developing egg-eaters. However, to be safe, crushing the shells or running through a blender is a good idea.

    Chicken birds and bees
    • The only reason a rooster would be required with a flock of hens is to fertilize eggs. As a side job, a good rooster also serves as a watchman, warning his hens of predators and other dangers. He also seeks out food for his harem.
    • Even with a virile rooster in residence, not all eggs will be fertile. Some hens just don’t interest a rooster and others never get caught. Often, roosters will have favorite hens that get most of their attention and others remain unnoticed.
    • Hens do not have an estrus cycle. They can mate and develop fertile eggs at any time.
    • Sperm can remain viable in the hen’s oviduct for three to four weeks, so one mating will fertilize numerous eggs.


    Brooding and hatching
    • A broody hen of any breed can be used to hatch eggs and raise chicks from other hens of any breeds.
    • A broody will sit on any eggs, whether or not they are fertile and regardless of who laid them. To gather a suitable clutch of eggs, she will not only lay her own eggs but may roll other hens’ eggs into her nest.
    • While a hen is brooding, you can remove daily any extra eggs she gathers into her clutch. Drawing pencil “equator” lines around the eggs you want her to brood will help with identification.
    • A setting hen will usually leave the nest at least once a day to eat, drink, and defecate. The eggs are not in danger of cooling off too much during a normal foray into the coop or run.
    • Typically, chicken eggs hatch about 21 days from the beginning of incubation or nesting by a broody hen. A few days early or late is not unusual, and some breeds lean toward earlier or later hatches.
    • Not all fertile eggs will develop into embryos. Some never develop due to egg deficiencies or temperature fluctuations.
    • Not all chick embryos will successfully hatch. They can die any time before hatching, even after pipping a hole in the egg. Double yolk eggs rarely hatch due to crowding during embryo development.
    • If a broody hen has pushed an egg out of the nest, she probably knows something is not right with that egg or embryo.


    In the kitchen
    • A normal fresh egg has a yellow yolk, a layer of thick albumen (egg white) surrounding the yolk, and a thinner layer of albumen surrounding that.
    • At opposite sides of the yolk are two chalazae, short white twisted strands of albumen that anchor the yolk to the white. A large chalaza does not indicate embryo development.
    • Every egg yolk has a white disc called a blastoderm. It is usually visible but may be very pale. In an infertile egg, the blastoderm is solid white. In a fertile egg, the disc has a faint or distinct ring that makes it look like a donut or bulls-eye.
    • Fertile eggs are completely edible. In fact, some people consider fertile eggs more nutritious than infertile eggs, but scientific research does not confirm this.
    • Fresh fertile eggs collected daily will not have embryos in them. Embryos do not begin to develop unless the eggs are in a favorable warm environment under a broody hen or in an artificial incubator.
    • The yolk of a chicken egg may be any shade from pale yellow to orange, depending on what the hen has eaten. The color is usually consistent if hens are fed only one type of feed, but foraging hens and those fed kitchen scraps will often produce a variety of yolk colors.
    • The egg yolk or egg white may have red or brown specks in it. These “blood spots” and “meat spots” are harmless bits of tissue and are allowed in commercial Grade B eggs. If they look unappealing, the spots can be removed with a spoon or knife before cooking.
    • An eggshell has a protective coating that prevents bacteria from entering the egg. To retain this coating, eggs should not be washed until just before use.
    • Some eggs are soiled with blood from minor tissue damage or mud or feces from the nest box. This can be wiped off carefully; the shell should be thoroughly dried.
    • If you aren’t sure how old an egg is, you can submerge it in water. The freshest eggs will remain at the bottom of the container, while old eggs will float. Floaters should either be discarded or opened far from your nose.

    That’s about all I know about eggs. Now maybe you can help me answer one more question.

    How can I get my hens to lay golden eggs? Those geese owners have it made.

    Further recommended reading:

    - Chicken Behaviors and Egglaying (Forum section)
    - Cleaning and storing fresh eggs
    - Common egg quality problems
    - Egg Color Chart - Find Out What Egg Color Your Breed Lays

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    Papa John59, 007Sean, terrig and 71 others like this.

Recent User Reviews

  1. 007Sean
    "Good article"
    5/5, 5 out of 5, reviewed May 3, 2019
    Very well written, easy to understand. Great knowledge for the beginner.
  2. jsr5
    "Great information."
    5/5, 5 out of 5, reviewed Apr 27, 2019
    I found this to be quite interesting and informative. Thanks!!
  3. Wi_Pida
    "Very interesting facts!"
    5/5, 5 out of 5, reviewed Mar 29, 2019
    I never thought to even looking into the information you provided. The only thing I looked into "lash eggs", which is an inflammation of the oviduct where the eggs begins its travels. They are not true eggs but may contain bits of egg material and a lot of pus and other material. They are rather disgusting and odd. If you want to see one I've attached a pic.


    1. wrinkled-eggs-web-388x294.jpg


To make a comment simply sign up and become a member!
  1. rocketmail
    This is by far the best and most informative article regarding information about eggs that I've seen before. You did a great job!
      Skipper81 likes this.
  2. trishminis3
    Great info. thanks. Tx
      Skipper81 likes this.
    Nice information! (I like the question at the end the best!)
      Skipper81 likes this.
  4. cluckcluckluke
    Great article. Top read!
      Skipper81 likes this.
  5. sunny & the 5 egg layers
    Fantastic Article! Well written and very informative.
  6. BirdbyGavin1103
    One of my girls need to read "normal do not lay at night." I went to check on the flock around 0300 this morning, since my dogs were doing their "you don't belong here bark," and found a double yolker broken on the poop board under my one leghorn. I know it wasn't there earlier as I check every morning, several times through the day and before lockup at night. They just started laying so I hope this isn't going to be a regular occurrence with her.
    Thank you for a great read, and my son loved learning some of the facts. Thanks again! I'll be saving this for future reference.
  7. Mrs. Mucket
    @Kelley Farms--There is a lot of variation in egg sizes. Some pullets seem to start right out with large eggs while others take a while to get it down. Most often the first eggs are small and they gradually increase in size. Your pullets are still young and it sounds like they are right on track! I'd say you could expect consistent sizes within a couple of months. Maybe other readers have answers as well?
      Skipper81 likes this.
  8. KayTee
    Everything you could ever want to know about eggs in one informative, interesting and well-written article. Thank you!
      Skipper81 likes this.
  9. ECSandCCFS
    Thanks for the info! Our pullets haven't started yet, so this will be useful now and later!
  10. LuvOurChickies
    Wonderful ! Thanks for sharing !
  11. Kourtnie
    Thanks for the great info!!!
  12. Kelley Farms
    When do your new layer hen egg size start getting bigger.. I've had few peewee but mostly small and a few mediums. in 2 weeks I have collected a dozen xl-jumbo but most are small size. at what week do pullets start laying a nice large egg? I have 22 pullets they were born feb15-20. Love the article.. have saved it.
  13. chickenalia
    enjoyed this article very much thankyou
  14. bornnraised
    great for newbies
  15. bornnraised
    great for newbies
  16. Nutcase
    Very good article! This is something I'll keep coming back to....
  17. Mrs. Mucket
    To ADozenGirlz and other readers: I apologize if my culling suggestion came across as insensitive. I had never noticed that BYC was mostly pet chicken owners, as most of my communication here has been with those who, like myself, raise chickens for eggs and meat. ADozenGirlz has some great suggestions for those who have space and time to rehabilitate an egg eater.
    A reader emailed me about the white hen with the blue face. She is a banty Silkie, our best mama who patiently sets on eggs and raises chicks with delight. Last year she and her BFF, a banty Dark Brahma, adopted 17 hatchery chicks and raised them together.
  18. ChickiesNSA
    Well written and very well organized, Great information! Thank you.
  19. chickenbusiness
    I did not know that a bulls eye meant that an egg was fertile. Wow, thank you for the article.
  20. girls and guineas
    Very helpful and interesting!! Thank you!!! Learned alot, and it answered alot of my questions!!
  21. Chickenfan4life
    Awesome article filled with great info!
  22. Too Fast
    Thanks for the article. I just read the whole thing, we will be new to BYC Spring 2013.
  23. Marty1876
    Still a great article!
  24. FowlmouthChick
    This article has been tremendously helpful! Thank you so much for posting.
  25. ChickadeeRanch
    Marans lay golden eggs!
  26. lakegirl1
    Thanks for the great information.
  27. chickenbusiness
    Great information! Thank you!
  28. trooper
    I really like this subject.There is more to the egg than meets the eye.Keep the info coming.
  29. myyardgirls
    great article ! easy to read and packed with info...thanks for contributing..
  30. outdoorsii
    awesome article :)
  31. mfpif16
    really cool! I don't have any roosters, but this stuff is good to know in case I ever get one, besides, it is also really interesting!
  32. sophiesmith
    Love the pic of the silke in the nesting box
  33. craftydrae
    fabulous!!! thank you so much! :)
  34. iron chicken
    very infromational, oh and GOLDEN EGGS!!!!!!!!!!!!!!!!!!
  35. ADozenGirlz
    This article suggest culling an egg-eater, which seems harsh and extreme. The BYC audience consists of primarily backyard chicken-keepers who view their chickens as pets, not livestock. A more balanced approach would offer suggestions for identifying the cause of the problem (eg: protein deficiency, boredom, too few nest boxes causing egg-breakage, calcium deficiency, etc.) and ways to rehabilitate an egg-eater, which is entirely possible by use of dummy eggs, collecting frequently, filling blown eggs with mustard and placing in the nest.
  36. DebbieParker
    Now that it is fall I am finding far less eggs to collect than I did this summer. My chickens have also found a way to get out of the fence and roam the woods, so we aren't sure if they are laying in the woods or if this is normal for production to drop drastically this time of year. They are not molting as they are only 7 months old.
  37. Dawna
    Thanks for the info. My hens have laid some unusual eggs and your article has given me answers. Thanks again.
  38. mo puff
    do goose lay an egg every day?
  39. ADozenGirlz
    Culling a bird from a flock for egg-eating is harsh and extreme. The BYC audience consists of primarily backyard chicken-keepers who view their chickens as pets, not livestock. A more balanced approach would offer suggestions for identifying the cause of the problem (eg: protein deficiency, boredom, too few nest boxes causing egg-breakage, calcium deficiency, etc.) and rehabilitating an egg-eater, which is entirely possible by use of dummy eggs, collecting frequently, filling blown eggs with mustard and placing in the nest.
  40. 1hotmoma
    Great article!
  41. clucky3255
    WOW.. it is interesting..
  42. Ullie
    thanks this is great!
  43. Chicks Galore3
    This is very helpful! great job!
  44. blondiebee181
  45. 6peeps
    just started getting eggs thanks for the info
  46. TW1Kell
    As everyone stated, "egg"cellant info article. I learned quite a bit from you.
  47. JustMaybe
    thanks this was very helpful to a person considering raising chickens.
  48. rosebuds
    u gave us a lot of info on how eggs are formed and what is needed to keep chick and shellshealthy
  49. GNB1991
    Very much enjoyed reading this article and sharing some new information with my husband! thank you!
  50. Marty1876
    Nice article. Very informative to all.

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