Ever wonder why eggshells have odd bumps or discolorations? Learn how eggs develop, and troubleshoot eggshell problems with chicken owner and writer Elizabeth Diane Mack.
For small poultry flock owners, eggshell abnormalities can be a bit scary. The internal shell development process occurs in less than 24 hours, and during this time, even minor upsets can affect the final eggshell quality and appearance. If you understand what irregularities indicate, you can decide if you’re seeing a temporary fluke, or if you need to treat your bird for nutritional or health issues.
Egg Development 101
Despite how quickly eggs develop (over the course of 25 to 26 hours), the process is quite complex. Young pullets (female chickens) begin life with two ovaries. As the pullets grow into laying hens, the right ovary doesn’t develop, while the left one becomes fully functional. Pullet chicks are born with tens of thousands of ova (yolks). Only a small portion of those ova will develop into eggs, and no new ones will develop as they mature, so chicks are born with the maximum number of eggs they’ll be able to lay.
Reproductive tract of a female chicken. Photo by Dr. Jacquie Jacob, University of Kentucky
A hen’s reproductive tract contains two major parts — the ovary and the oviduct. As the pullet matures, the yolks slowly develop, receiving nutrients from attached blood vessels. As an immature yolk grows to about the size of a quarter, the yolk is released from the ovary. During this stage, a hiccup in the process might occur, resulting in a harmless blood spot on the yolk. If a hen releases two yolks, you’ll have a double-yolked egg.
The yolk then enters the oviduct, where eggshell production commences in the 2-foot-long internal assembly line. The released yolk is first picked up by the infundibulum, or the funnel, where the yolk enters into the oviduct and stays for about 15 minutes. The yolk then travels to the magnum, remaining there for about 3 hours. The burgeoning egg then gets its egg white protein, or albumen, by rotating through the magnum as strings of albumen are twisted around the yolk. These “chalaza” strings center the yolk in the finished egg.
During the next stage of the process, the inner and outer shell membranes are added to the developing egg in the isthmus. The yolk remains in the isthmus for about 75 minutes before traveling to the final stop in egg production, the shell gland, or uterus. The majority of the egg assembly time (20 or more hours) is spent in the shell gland. Calcium carbonate is diverted from the chicken’s bones to provide about 47 percent of the shell, while feed nutrients provide the rest. This is why adding oyster shell or other calcium sources to your chicken’s diet is so important. As the outer shell hardens, pigment is also added before the egg moves into the vagina. “Bloom” or a thin cuticle layer, is added, and the vaginal muscles turn the egg to push it out large end first.
Egg Shell Irregularities
Throughout this process, events can occur that result in irregular shells: anything from pimple-like bumps and wrinkles to a shell-less egg. Irregularities can occur naturally, but they can also signal that your chicken is having health problems.
If you notice eggshell irregularities happening consistently, you should consult a poultry vet. According to Dr. Jacquie Jacob, a poultry extension associate at the University of Kentucky, eggshell abnormalities can be the result of many things, including disease. “It can be something mild, like infectious bronchitis, or something serious, like Newcastle disease.”
But, Jacob says, before you consult a vet, look at nutrition first. “A lot of people feed a layer feed diluted with scratch grains or cracked corn, and nutritional deficiencies occur. Shell-less or weak shells could be calcium, phosphorus, magnesium or Vitamin D, or even a protein, deficiency.” Jacob adds that heat stress and even rough handling can cause shell problems as well.
Small flock chicken keepers should take note of specific shell abnormalities to distinguish between simple aesthetic oddities and signs of serious health issues.
Shell-less Eggs
Young hens coming into lay for the first time might lay a shell-less egg or two. In mature hens, it’s also not uncommon to find a shell-less egg under the roost. While finding this water-balloon type of egg can be alarming, it doesn’t necessarily indicate any major health problems.
Shell-less membrane passed overnight. Photo by author.
A shell-less egg is just like it sounds. While the membrane forms around the yolk and egg white, the shell doesn’t. A shell-less egg can be a sign of nutritional deficiencies, such as missing calcium, phosphorous, or vitamin E or D. If added nutrients fail to solve the problem, shell-less eggs could indicate infectious bronchitis (IB) or egg drop syndrome (EDS). IB is an extremely contagious viral disease, so the entire flock would have symptoms, and not just one bird. EDS is also a viral infection that will typically affect more than one bird.
Shell-less eggs can also occur toward the end of winter or the end of a molt as the egg-laying “factory” is getting back up to speed. Sometimes, a shell-less egg can even occur if there was a disturbance at night, such as a predator sniffing around the coop.
Soft-shelled or Rubber Eggs
Similar to shell-less eggs, soft-shelled eggs occur when the shell doesn’t fully form around the yolk and membrane. The membrane is thick enough to hold the liquid in, but lack the calcium of the hard shell. You can pick up a soft-shelled egg by pinching the outer membrane between two fingers, like a deflated water balloon. If soft-shelled eggs appear in the heat of the summer, heat stress could be to blame. Many chicken breeds, such as the heavier Orpingtons and Wyandottes, don’t tolerate excessive heat well. Fresh water in the summer months is essential to avoid shell abnormalities and other health problems, but make sure it’s unsoftened water. While inadequate nutrition is sometimes to blame, this irregularity is more often caused by excessive phosphorous consumption.
Corrugated Shells
These corrugated shells were a temporary issue. Photo by author.
This rough, irregularly ribbed appearance can be caused by a variety of external factors. Heat stress, salty or softened water, poor nutrition, or vitamin D deficiency can cause these weird, wavy ridges. While older laying hens are more likely to produce corrugated shells, mycotoxins, the byproducts of toxic organisms sometimes found in poultry feed, can also be to blame. If you’ve recently changed feed or your feed is old or moldy, try remedying this first. Make sure the water you use hasn’t been “softened” or treated with lime, resins, salts, or chelating agents.
Wrinkled or Rippled Shells
A few deep wrinkles were accompanied by pale shells. Photo by author.
If the egg’s albumen, or whites, are underdeveloped and watery, it’s difficult for the shell to develop normally, which can result in what appears to be wrinkled shells. As a hen ages, it’s normal for the white to become thinner, which can lead to a rippled outer shell.
However, when younger hens continually lay wrinkled eggs, it could be a sign of infectious bronchitis, as IB prevents the hen from producing a thick albumen. If the hen has a good diet with plenty of nutrients, is not overcrowded or stressed, and appears healthy otherwise, an occasional wrinkled shell is nothing to worry about.
Calcium Deposits or Pimples
Calcium deposits. Also note the irregular shape on the narrow end. Photo by author.
Calcium deposits can take the form of hardened masses or fine, sand-like particles that can easily be brushed off. Calcium deposits can often be attributed to a disturbance during the shell calcification while in the oviduct. Common disturbances include a predator, loud thunderstorms, or a bully hen. While it’s possible that excess calcium in the diet could be a factor, it’s not as common. As with many other shell abnormalities, a defective shell gland (uterus) could also be the cause.
Pale Shells
Different chicken breeds lay eggs in every color of the rainbow, from Leghorn pure-white, to Welsummer and Maran dark-brown. But what about when a layer that normally produces brown eggs lays a pale one? The eggshell’s pigment is deposited in the shell gland pouch. If the shell gland is defective in any way, the quality of the pigment is affected. While it’s not uncommon for older hens to lay pale eggs, younger layers whose eggshells are abnormally pale might be suffering from infectious bronchitis.
Misshaped Eggs
Round-shaped shells, elongated shells, football-shaped shells, or any shape different from the oval norm are all considered misshaped. Irregular shapes are more of a concern in large egg production, as consumers expect their eggs to be uniform and perfect. Overcrowding and stress can cause abnormal shapes, as can several diseases. If you’re noticing misshapen eggs regularly, have your vet test for diseases such as avian influenza, infectious bronchitis, and Newcastle disease.
Body-checked Egg
A shell with a pronounced “belt,” or extra shell layer around the middle, occurs when a cracked shell in the oviduct forms a layer of calcium carbonate, creating a noticeable raised ridge around the center of the shell. While older hens experience a higher incidence of body-checked eggs, this abnormality can also be caused by stress or overcrowding in the coop.
When to Seek Treatment
In a small, backyard flock with a good diet and adequate clean water, the most common causes of shell irregularities are overcrowding and stress. If a predator frightens a laying hen, the passage through the oviduct can temporarily halt. This delay can result in additional calcium carbonate deposited onto the shell, causing a ridged waist, papery-thin shells, or other irregularities. Sometimes, there isn’t any clear cause of a single misshapen egg.
Irregular shells are a larger problem for large-scale production, as an abnormally shaped egg won’t easily fit into an egg carton and may be more prone to breaking during transportation. If you’re hoping to hatch chicks, you should avoid using abnormally shaped eggs, as sometimes the shell problems are hereditary.
If you notice consistent egg abnormalities over several days or weeks, you should check with a vet about possible illness in your flock, especially if more than one hen seems to be affected.
A hen who receives a healthy diet of good-quality layer feed and oyster shell, who shows no symptoms of respiratory illness, and who enjoys plenty of safe room to roam, may still lay the occasional odd egg. These problems are temporary, and the eggs are safe to use. So enjoy your eggs.
Freelance writer Elizabeth Diane Mack keeps a small flock of chickens on a 2-plus-acre hobby farm outside of Omaha, Nebraska. Her work has appeared in Capper’s Farmer, Out Here, First for Women, Nebraskaland, and numerous other print and online publications. Her first book, Healing Springs & Other Stories, includes her introduction — and subsequent love affair — with chicken keeping. Visit her website at BigMackWriting.com.
15 Comments
I have a nearly 3 yr old hen that is a good layer. But since her last molt she lays with a very thin shell and is usually broken. She sometimes needs help expelling the shell. They have oyster shell available and I bake and crush their shells and feed them back to them. Any suggestions?
A couple questions for you.
1. We have two young pullets that started laying about 2 months ago (Buff O’s). There eggs have matured from small to large in that time and the shells/eggs look good. However this past week one of them is laying eggs that are very greasy. The egg has an oily substance all over it as well as having some sort of debris. Two days ago the egg was greasy with a smear of black on it which I assumed was a bit of poo. Yesterday it was still oily, but less and todays egg is still oily but with a small amount of yolk color debris on it…any idea what this is?
2. Is there a way to tell which chicken lays each egg?
We also. have a Buff O Cockerel (it was supposed to be a pullet) and 3-3 1/2 y/o Dark Brahmas that quit laying last summer (that is why we got the O’s). The cockerel mounts the two young pullets often so I don’t know if that has anything to do with the oily substance.
I am not new to chickens, just oily eggs and a cockerel!
Appreciate your advice. Thanks!
The egg shell is also weird when the chicken had too much potatoes (or starch), please, add the pictures of such cases
I have one hen (out of ten) who lays corrugated eggs. All the other hens lay normal eggs, so I am not sure what she has? I think she is also the hen who does not lay very often. So, I am not sure if she lays normal eggs in between the corrugated or not. Any suggestions?
HI I have had 4 chickens now for over 7 months and laying every day… however yesterday one laid an egg that looked like the first time they laid an egg… rubbery and then today one egg was covered in what looks like scars across it … can you help ???
Hi Angelique,
Email me at ctilghman@ogdenpubs.com with some pictures of the eggs and let’s see what we can figure out.
I’m getting very hard and brittle eggshells and the shell inner liner is very thick and hard to rip open to remove the egg.
Several pieces of eggshell will fall into the pan/cup when attempting to remove the egg from the shell. Please Help!
Hi William – Without knowing a lot of specifics, I can only guess. If ALL chickens are laying hard-shelled eggs, first look at what they’re eating. The feed (and water) is one of the biggest components of how the eggshells will develop. if you are using quality layer feed of 16% protein for layers, that should be good.
If you offer oyster shell, it should only be offered individually in its own container, and not mixed with feed. They’ll eat it only if they need it.
If your chickens are young layers, the eggs may be smaller, so might be harder in the beginning. Often overly-hard shells will often solve itself as they mature.
Actually, this is a rare issue. Usually the opposite is the problem. Good luck.
Hi, we’ve had two large eggless shells this yr. I suspect heat stress. It has been in mid 90s with heat index 105-109. I’ve been freezing organic peas, corn and strawberries and giving them during peak heat. They have “cool” places under the deck and in the woods surrounding property. They get oyster shells at will, sand and quality layer pellets as well as free range from 9 am until they roost.
My question is how do I provide vitamin E and D? They also get fresh water, in the shade and in three different spots all over the property. I may already have it covered with feed, but this is just weird to see two eggs within 4 months missing the shell. They are fully developed and we can pick them up. Describing them like water balloons is perfect. Thanks in advance!
Thanks for reading Eadie! If your flock is getting quality layer feed, you shouldn’t need to supplement, except for the oyster shell. I might suggest to avoid the corn if they’re having problems (the corn has no nutritional value). An avian vet recommended that I not feed my flock treats if they’re having any shell problems. However, the vet did recommend offering spinach or kale greens, and scrambled eggs with ground shells. I have an Australorp that has passed a soft-shelled egg about once a month for 4 years, since she started laying, with no other issues. Just a fluke in her system somewhere.
Elizabeth
Awesome article. I learned a lot about egg production. Thank you
Thanks Marilyn! Glad you enjoyed it.
THANK YOU for this incredible information!!! I’ve been having several of these issues in my little flock and couldn’t figure out what was going on and what to do. This is EXACTLY the information I needed. THANK YOU THANK YOU!
Our pleasure sharing Elizabeth Mack’s article with you. (Personal note: I thought the same thing when I read the article draft: “That’s what’s wrong with those eggs!!!”) Good luck.
Nice informative article on eggs and eggshell problems! And great pictures too! Thanks so much for the info 🙂