Best Of Bitchin' Chickens Eggs Health Issues

Weird Eggs 101: The Oddities Explained (Or What’s A Fart Egg?!)

Before I had chickens I probably didn’t give a lot of thought to how eggs are actually made. That all changed post-chickens: it takes many months till those little chicks grow up and begin to lay, and in the interim there’s a lot of anticipation as to what kind of egg I’ll be surprised with in the nest box. For the most part, I breed crosses so there’s no predicting what colour I might find. Once I started looking into the actual logistics of what goes into making an egg I was blown away. It’s a small miracle that birds produce something so complex.

If you buy eggs from a store they are graded and those with imperfections aren’t sold. Once in a while you might see flaws in a farm egg, but most people just take eggs for granted.

Today we’re going to talk about egg oddities, but before we get into the weird stuff here’s a quick 101 on How An Egg Is Made:

Think of a hen’s reproductive tract as being like a conveyor belt with various components of egg production happening at different stations. The first part of the egg,  the yolk, is made in the ovary and when it reaches the right size it’s released into the infundibulum. This is one end of a long, spiraling tube called the oviduct. If there is sperm present this is where fertilization takes place during a short window of opportunity before the egg moves on.

Next stop: the magnum, where the albumen (egg white) is added. As the egg goes down through the oviduct, it is continually rotating. Chalaza – strands made of twisted tightly albumen – form to keep the yolk in the middle of the egg and prevent it from sticking to the inside of the shell. There are two chalazae anchoring each yolk, on opposite ends of the egg.

It travels to the isthmus for the addition of shell membranes. The developing egg spends most of its time in the shell gland where the shell (calcium carbonate) and any shell pigments are added. As the egg is being assembled it travels down the oviduct small end first. In the vagina it is pushed out the large end first, preventing the egg from being contaminated by fecal material when it is laid. That whole process takes about a day. Since many hens lay several times a week the conveyor belt has a number of eggs, at different stages of development, at different stations along the way.


I have, over the years, had a few odd eggs but don’t have lots of photos so I put a call out to friends of Bitchin’ Chickens and was not disappointed with what I received.

Here’s a sample and the lowdown on some egg oddities:

Double yolks commonly occur in new layers when yolk release is mistimed and two yolks travel down the oviduct together. Older hens tend to lay larger eggs because the oviduct loses elasticity over time. A double-yolker rarely hatches. A triple-yolker is really rare.

Eggs with no shell feel rubbery because the membranes are on the outside. These irregular eggs are commonly produced by new layers, but can result at any time from stress or often from calcium, phosphorous or vitamin D deficiency.

High environmental temperatures are the most common cause of thin-shelled eggs. A hen’s increased rate of respiration interferes with calcium carbonate production and shell formation. Older hens generally produce thinner shells as their oviducts wears out.

Egg shells can have different textures caused by a number of factors: excess calcium (pimples that can be scraped off) or vitamin D intake to double-ovulation, disease, a defective shell gland or rapid changes in lighting (sandpaper shells).

When an egg is delayed in the shell gland, a second egg coming down the oviduct will bump into it and rest alongside the first egg, causing a flat, wrinkled side. These are called slab sided eggs.

Oddly coloured eggs are the result of being unevenly pigmented while in the shell gland pouch.

An egg within an egg occurs when, for some unknown reason, an egg almost ready to be laid reverses and backs up into the reproductive tract, where it meets the next egg in progress. The first egg receives more albumen, membranes and shell before being laid. The one on the right is not only an egg-within-an-egg, but one received the blue pigment and the outer shell did not.

Tiny eggs, sometimes containing no yolk, are referred to as fairy, wind, or fart eggs. (I don’t make this stuff up!) These irregular eggs are also common in new layers when the reproductive system is not yet synchronized, but can also occur in older hens when a piece of tissue from the oviduct breaks free, tricking the hen’s reproductive system into treating the tissue like a yolk and creating an egg.

Shells with slight cracks have been damaged while in the shell gland from stress or pressure. You can see how the cracks have been repaired before they were laid. Wrinkled eggs are often associated with respiratory infections, like bronchitis.

These ones usually occur while the hen is laying the egg, which then gets stuck, creating a little tail. Some of these are soft-shelled eggs which harden post-hatch.

Egg With A Tail
Egg With A Tail

In pullets, an immature shell gland can cause odd-shaped shells and is usually not problematic. In older hens, oddly shaped eggs can result from stress or, if they are a regular occurrence, a defective shell gland often caused by infectious bronchitis.

This is an interesting one laid by a hen who was previously egg bound. The soft-shelled  egg on the right was followed by the ‘lash egg’ on the left. It’s not an egg but a by-product of a salpingitis infection.

Christie Miller eggbound, then soft with lash

People see all kinds of religious imagery in clouds and on their morning toast, here’s Eeyore on an egg.


This is one of my favourites: One large egg when broken open revealed not just three yolks, but one tiny fart egg complete with shell!

3 yolks, 1 fart

Occasionally I get some of these types of eggs, but you’re unlikely to see them. Usually only double-yolkers make the cut for quality control for you, my paying customer. We, the farmers, eat the oddities – the shells may be imperfect but those little orbs are perfect on the inside.


Photos courtesy of Bitchin’ Chicken friends: Agnes Laan, Angela Spooner, Cas, Cheryl Handlen, Christie Miller, Connie Haslam Green, Courtney Kemp, Dawn McQuinn, Deanna Dunlop-Muise, Elizabeth Campbell, Jenn Hobbs, Kathy Williams, Kay Ervin, Laura Turner, Liza Jane, Marie Clark, Megan Hourd, Melissa Bodden, Minda Dimond, Rachel Leek, Shannon Briggs, Terra Strachan & Trent Biggs.

4 comments on “Weird Eggs 101: The Oddities Explained (Or What’s A Fart Egg?!)

  1. Great info & photos to prove that sometimes truth is stranger than fiction!


  2. I’ve found plenty of strange eggs in my coop, and most of them have come from one of my three year old hens…Is that normal?


    • Yes. I think we’re trained by store-bought eggs to think of them as always being perfect, but there’s a real range of what is considered normal. As hens age there are changes in their reproductive systems (i.e. uptake of calcium, hormonal issues etc) that can affect the appearance of their eggs.


  3. Betty J. Cogley

    This is so interesting! Thank you and the folks you got the pictures from. I’ve had chickens for years and an always blown away by their antics, personalities and of course, the eggs.

    Liked by 1 person

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