An EGGcellent Surprise!

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I just came in from gathering eggs, and I was a bit surprised to find that one of them was gigantic! Our chickens have just started laying, so most of the eggs we get are a bit small, but this one was more like extra large size.

The Beast

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I immediately suspected that something was up. I don't know if it was intuition or maybe it was just the extra size and weight of the thing, but something told me that this was going to be a double yolked egg.

Science & Superstition

Before we crack this thing open, you may be wondering how a double yolk egg forms or if there is any significance to it.

The Science

To understand how they form, you first need to have some understanding of how the chicken reproductive system works. Right from birth, a chicken already has all of the eggs it will ver lay stored within her two ovaries. But then, some time before she reaches sexual maturity, one of those ovaries (almost always the right one) shrivels up and becomes nonfunctional. So, every egg that a chicken ever lays will come from here left ovary.

You may be wondering, "How do all of those things fit inside a chicken?" The answer is pretty simple: a chicken egg doesn't start out looking like those things in your refrigerator. They begin as tiny little yolks or follicles as they are called. Each follicle has a tiny speck on it; an oocyte or immature egg cell that may one day be fertilized and grow into a new baby chick. Now, remember there is a follicle inside of the chicken's ovary for every egg she will ever produce, so they have to start out pretty small.

Follicles In The Ovary

Min Kang, Se-Yeoun Cha, and Hyung-Kwan Jang, Changes:Revivalz1, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

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Notice in the picture above that some of the follicles (the tiny ones) have yet to even begin developing, while others are in different stages of maturation. The larger the yolk is, the more mature it is and the closer it is to being passed on into the oviduct.

Once a yolk is released into the oviduct, it will spend about 25-27 hours traveling through and picking up the albumin (egg white) Finally, the hen will lay her egg. Often times, especially in a heavy laying breed, the next yolk will make its way into the oviduct with an hour or so, and the process will repeat.

But Why The Double Yolks?

A double yolk egg forms when two yolks get intertwined in the same blob of albumin and then packaged together in the same shell. This is not as rare of an occurrence as you might think, happening in an estimated 1 in 1000 eggs laid. But, you can greatly increase those odds if you are raising a young flock. The chicken reproductive cycle is driven by hormones, and in a young pullet (especially those less than 1 year), those hormone schedules may not be quite ironed out. This may lead to two yolks being released close enough together in time to both get caught up together when the albumin starts flying. Alternatively, a double yolker may also form due to mechanical means. I have read that it is not all that uncommon to find little chinks of meat floating around in the albumin of an egg. Again, this is most common in young pullets. Those little meat chunks are actually little pieces of the oviduct that have sloughed off while the egg was moving through. This raises the possibility that obstructions within the oviduct may slow down the progress of one yolk, allowing time for the next yolk to catch up with it before the shell gets put on.

Now, do note that this is a highly simplified explanation of the chicken reproductive system. If you would like a much more comprehensive study, I recommend you check check out PoultryHub.org's page on the topic.

The Superstition

If you are the superstitious type, then you might be interested to learn that there is quite a lot of folklore surrounding eggs. You may even recall my earlier post regarding Fart Eggs.

Double yolk eggs have carried a few different cultural connotations. In Norse tradition, they were an omen of death. However, most other cultures attributed more positive vibes to their double yolkers. Many saw them as bringers of good fortune or more commonly, fertility. Either someone was going to get pregnant or possibly have twins!

The Grand Reveal

So, now that you've learned a little bit about double yolked eggs, you're probably pretty anxious to know whether our giant chicken butt nugget is one of them. To find out, you'll have to watch the video...

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SOURCES

1) https://poultry.extension.org/articles/poultry-anatomy/avian-reproductive-female/
2) https://www.betterhensandgardens.com/what-causes-double-yolks/
3) https://www.foodandwine.com/breakfast-brunch/eggs/your-questions-about-double-yolk-eggs-answered
4) http://www.poultryhub.org/physiology/body-systems/reproductive-system/#:~:text=The%20appropriate%20signal%20for%20this,the%20development%20of%20the%20oviduct.
5) https://theconversation.com/ive-always-wondered-can-two-chickens-hatch-out-of-a-double-yolk-egg-94165#:~:text=They%20are%20created%20when%20two,shows%2C%20can%20be%20bred%20for.