Interesting Facts About Chicken Eggs

Eggs are amazing things. We often take them for granted, but you won't after you read this article!
  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.

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  1. 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.
  2. chickenalia
    enjoyed this article very much thankyou
  3. bornnraised
    great for newbies
  4. bornnraised
    great for newbies
  5. Nutcase
    Very good article! This is something I'll keep coming back to....
  6. 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.
  7. ChickiesNSA
    Well written and very well organized, Great information! Thank you.
  8. chickenbusiness
    I did not know that a bulls eye meant that an egg was fertile. Wow, thank you for the article.
  9. girls and guineas
    Very helpful and interesting!! Thank you!!! Learned alot, and it answered alot of my questions!!
  10. Chickenfan4life
    Awesome article filled with great info!
  11. Too Fast
    Thanks for the article. I just read the whole thing, we will be new to BYC Spring 2013.
  12. Marty1876
    Still a great article!
  13. FowlmouthChick
    This article has been tremendously helpful! Thank you so much for posting.
  14. ChickadeeRanch
    Marans lay golden eggs!
  15. lakegirl1
    Thanks for the great information.
  16. chickenbusiness
    Great information! Thank you!
  17. trooper
    I really like this subject.There is more to the egg than meets the eye.Keep the info coming.
  18. myyardgirls
    great article ! easy to read and packed with info...thanks for contributing..
  19. outdoorsii
    awesome article :)
  20. 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!
  21. sophiesmith
    Love the pic of the silke in the nesting box
  22. craftydrae
    fabulous!!! thank you so much! :)
  23. iron chicken
    very infromational, oh and GOLDEN EGGS!!!!!!!!!!!!!!!!!!
  24. 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.
  25. 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.
  26. Dawna
    Thanks for the info. My hens have laid some unusual eggs and your article has given me answers. Thanks again.
  27. mo puff
    do goose lay an egg every day?
  28. 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.
  29. 1hotmoma
    Great article!
  30. clucky3255
    WOW.. it is interesting..
  31. Ullie
    thanks this is great!
  32. Chicks Galore3
    This is very helpful! great job!
  33. blondiebee181
  34. 6peeps
    just started getting eggs thanks for the info
  35. TW1Kell
    As everyone stated, "egg"cellant info article. I learned quite a bit from you.
  36. JustMaybe
    thanks this was very helpful to a person considering raising chickens.
  37. rosebuds
    u gave us a lot of info on how eggs are formed and what is needed to keep chick and shellshealthy
  38. GNB1991
    Very much enjoyed reading this article and sharing some new information with my husband! thank you!
  39. Marty1876
    Nice article. Very informative to all.
  40. dutch girl
    Good to know. I am a newbie, lots of good info, thank you
  41. pkincaid
    For a newbie, this was incredibly helpful!
  42. blondiebee181
    Thanks so much! This was great!
  43. Shelby12
    Great:) Very informative, all my questions were answered through this article "Interesting Facts on Chicken Eggs. Thank you as I learnt things i did not know.
  44. garagegirl
    Thank you Mrs.Mucket that was helpful. I guess none of my hens are broody yet because they are only in their boxes to lay the eggs although I have found few on the floor.I will try another way of cooking next time. Thank you have a great day
  45. Mrs. Mucket
    KristinLLB--I'll see if I can add to the article. For now, here's some info: It is not necessary to wash eggs, but I usually do--especially soiled ones and those with debris on them. Eggs have a protective coating that prevents bacteria from entering, and washing can remove that. So I recommend washing just before use. Cold water is said to drive bacteria through the shell, so warm water is best. I either hold under running water or wipe with a damp cloth. Some states require washing before selling.
    Garagegirl--Those are good questions!
    Only a broody hen will sit on eggs to hatch them--if none of your hens are broody, that won't happen. It's best to collect the eggs so they don't get broken. If you do have a broody and you do want her to hatch eggs, you can leave eggs under her and as her sister hens lay more eggs she will pull them under her, too. I like to move the hen to a separate nest when she has the number of eggs I want her to sit on and hatch. An alternative is to mark the keeper eggs and remove all others from the broody hen. I once came home from a trip and found one broody hen overflowing with eggs she couldn't even cover! My helper didn't want to reach under her for eggs so she kept collecting them herself.
    Eggs can go straight to the pan or be stored at room temp or in the fridge. You can wash them as described above.
    Any bird over 16 weeks or so is likely to be too tough for frying or roasting. They are best stewed or slow cooked in water for several hours to tenderize.
  46. garagegirl
    Nice article,but I still have questions? Can I leave the eggs in the boxes and will the hens sit on them to hatch them? If I collect the eggs daily to eat can they go straight to my pan or are there any special things you do before you eat them? Also what is the best way to cook young rooster? We cooked two of ours and they were a little chewy as my 7yr old said. Thanks for your help have a great day.
  47. dutch girl
    Thank for the info, I am a newby so anything helps!
  48. KristinLLB
    that was really fun to read, and really informative! I request a small addition about how to wash eggs in the Kitchen section. I think a lot of newbies would be interested in that.
    Thank you!
  49. Phottoman
    I just wanted to add my thanks too. This was a very well written article, and I even read EVERY comment, and that's rare for me. I bought my first day old chicks eight weeks ago, so I have a L-O-N-G time to wait before getting eggs. But that's OK too since I am the only one in the family that can even eat eggs. And chicken math is happening here too, what started as two chickens is now 22 chickens, but I think I am done buying for a while. I just hope some of mine become broody.
  50. OnTheWing
    Great article - just found it! My pullets have just started laying so this was very informative!

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