Do Chickens Have Periods

Do Chickens Have Periods? (No, Here’s Why..)

Do chickens have periods? Are eggs chicken periods? Are you eating a chicken period when you’re eating eggs?

Saying that eggs are “chicken periods” is something vegans and organizations like Peta have been saying for some time to dissuade people from eating eggs.

The sad thing is that it’s a shock factor tactic to try and gross people out. Not a nice way to get a message across in my opinion.

If it’s bothered you or you’re interested to learn more, there are two things to consider;

First of all, you have to realize the motivation behind Peta and similar organizations. They don’t want people to eat eggs, so they will say whatever they think will make an impact to stop people.

Secondly, it’s just not strictly true. An egg is not the result of a chicken’s period. There are some key differences in the reproductive system between mammals (us) and chickens (birds).

Do Chickens Have Periods?

No, chickens do not have periods. This is explained in great detail by They state that only humans, our close relatives, and a couple of other animals have periods.

In fact, no other species than mammals have menstrual cycles, and even then very few mammals have them.

Chickens are a different species, they’re birds. They are not mammals or reptiles are often thought < I explain that in more detail in that post.

The Process of How Chickens Lay Eggs

The Process of How Chickens Lay Eggs

To better explain why chickens do not have periods – and how their reproductive system is very different from ours – I can give you a quick lesson in how chickens lay eggs.

First of all, chicken’s need certain environmental conditions to lay eggs. One such condition is sunlight, without sunlight, a chicken will not start the process of creating an egg.

This is because the laying process starts when light enters the hen’s eye. Doing so activates a photosensitive gland known as the pineal gland.

Once this gland is triggered by light – either artificial or natural – the process of releasing an egg, or oocyte, from the hen’s ovary starts.

The yolk is then released into the oviduct, a long tube that’s part of a hen’s reproductive system. This is when the egg will be fertilized if she’s successfully mated with a rooster.

Fertilized or not, the egg continues to travel through the oviduct where a membrane, structural fibers, the egg white, and finally the shell are added.

The entire process of laying an egg from start to finish takes between 24-26 hours. Which is why, with all the right conditions, you can expect one egg a day from prolific layers like Rhode Island Reds and Leghorns.

How Chickens Differ From Mammals

You’ll notice from the above that a chicken’s reproductive system and just the process of how they create eggs is very different from the human reproductive process.

The main differences are:

  • Chickens do not have menstrual cycles – there is no defined cycle to how and when they lay eggs.
  • The pregnancy process in mammals is very different depending on whether eggs are fertilized or not – for chickens, the process is the same, fertilized or not.

Hence, a chicken does not produce an egg because of a “failed” fertilization.

Why Do Chickens Lay Unfertilized Eggs?

The burning question I see asked so often is, “why do chickens lay unfertilized eggs?”

There are few answers to this question;

  • The first is simply because a chicken does not know if/or an egg will be fertilized, so they go ahead and go through the process.
  • Another reason is that as I explained above, their reproductive system is created in such a way that fertilized or unfertilized eggs go through (almost) the same process.

The answer that makes the most sense as to why chickens lay so many unfertilized eggs, is because they’ve been selectively bred to do so.

We’ve been making changes to chickens’ DNA for thousands of years at this point. Most of which for the purpose of making them and a better food source. Both for their meat and eggs.

They’ve been bred to better tolerate the cold/heat, develop more meat, and lay more eggs. While most wild birds lay very few eggs, and only during select times of the year.

In Summary

I’ve read plenty of blog posts by vegans and animal activists that are so against eating eggs that no matter how it’s explained to them, they’re not going to change their stance.

But the facts are, chickens do not have periods. Not in the same way as we and some mammals do, they’re just not able to do so.

If you’re against eating eggs, that’s fine. I don’t judge anyone for their beliefs. But if you look at the facts and the anatomical and scientific evidence, chickens are not having “periods” when laying eggs.


Image credits – Photos by Ben Greene and Daniel Tuttle on Unsplash

Egg and Embryo Development –

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