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.
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.
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.
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.
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
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 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.
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.
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.
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.