Lesson 446 – Double yolked eggs and other oddities

If you take one of my chicken workshops, then you learn how chickens form and lay eggs. The first thing I always do is draw a chicken oviduct on the white board. It’s not that hard to draw because essentially the oviduct is simply a long twisted tube.

So let’s start at the beginning. Roughly every 18 hours (more for some birds, a little less for others) a hen releases an egg. That’s the yellow part that is blamed for our cholesterol counts being high.

As it travels down the oviduct, a gelatinous membrane is added. That’s the white of the egg, also called the albumin and is the stuff of which lovely meringue is made of.

The egg then continues to travel down the twisty oviduct. Because it is being rolled over and over, the fibrous strands inside (called the chalaza) twist which helps to anchor the yolk within the albumin.

Once the egg reaches the lower portion of the oviduct, calcium is deposited around the egg creating the shell.

There are several things that can go wrong with this process and knowing how an egg is formed will help you determine where the problem is.

Double yolks – if you get a double yolked egg, it could be that:
Your hen just tends to release two yolks at one time, hey, it happens with humans, (twins) it can happen with chickens.
Another reason for double yolks is that the first yolk did not travel down the oviduct in time before the second yolk was released. This causes a little bit of a back-up resulting in two passengers taking the same cab (as it were.)

Multiple shelled eggs – sometimes the egg sits too long at the base of the oviduct. The calcium is applied but the egg doesn’t move out. This can result in an egg with multiple shells. We’ve had a few of these. Sometimes, it’s just another shell applied and sometimes along comes another full gelatinous egg that is covered along with the existing previously shelled egg.

As you can imagine, this is not a good situation. If multiple full eggs are covered (and you can see some of these on youtube) an egg can get very large. Sometimes too large and it can get stuck in the hen causing – you got it – a dead bird (who suffers for a long time before she dies.)

If the calcium mechanism is not working properly, an egg can pass through without a shell (we call them zombie eggs.) Although this is something that can happen on occasion, it would still be wise in this particular case to check if the birds are getting enough calcium in their feed.

For the most part, chickens know what they are doing. Heck, they’ve been at it for thousands of years. Sometimes things go wrong, sometimes things are not perfect, when you’re laying an egg every other day for a few years, you’re bound to have a few hic-cups.

So there you do, that’s my egg formation lesson. Attached is a photo of a double egg taken by someone who attended my workshop and who was able to explain to his wife exactly how this happened. A+ for you Stephan!

By the way, the last thing I do is this chicken -egg lesson is to erase the white board before I leave for the night because I’ve been yelled at by too many High School teachers for accidentally leaving a picture of a chicken oviduct in the Spanish room for the next day’s classes.

Seeing double (in the pan)



Filed under Backyard Chickens, Chicken talks, Reader's stories

3 responses to “Lesson 446 – Double yolked eggs and other oddities

  1. Hi Wendy,

    I like your article. Thanks for posting it. I haven’t heard of eggs with no shells being called zombie eggs before, but it’s appropriate. It could catch on.

    • Wendy Thomas

      Poultry Matters,

      You haven’t heard of zombie eggs? Clearly you don’t have four teenage sons living in your house. 🙂


  2. Our son collected his first double yolk a few weeks ago and still talks about his “Super Jumbo” egg.

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