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How Are Chicken Eggs Fertilized

chicken eggs are fertilized

We all know that you don’t need a rooster to get an egg, right? Our hens will lay an egg daily with or without any assistance from the male sex.

However, if you want fertilized chicken eggs, you will need a rooster to perform his duties with your hens, which he will be happy to do continuously.

A rooster is genetically programmed to take the task of populating the world with his offspring, and he is single-minded about it, dedicated even!

So today’s article is all about the fertilization process, how it comes about and how you can contribute to getting fertilized eggs.

Chicken Eggs Fertilized

Spring Fever – Mating Season

Courtship, mating, and raising brood starts in the springtime. The increase in daylight energizes the hormones, and the increase in hormones leads to procreation behaviors.

The pineal gland in the chicken’s brain detects the increase in light – this, in turn, stimulates the manufacture of androgen, estrogen, and progesterone – the hormones responsible for increasing egg production and broodiness.

These hormones, in turn, produce a cascade of other hormones necessary for the development of the yolk and the soon-to-be embryo.

You should remember that many of today’s chicken breeds have had the innate ability to become broody bred out of them, so few, if any, will sit on eggs for you. If you don’t have a broody hen, you will certainly need an incubator.

An interesting thing to note here is that broodiness is ‘infectious.’ If you get one hen to go broody, you will likely have at least one more of the ladies who want to brood!

Most of these ‘secondary’ brooders will not sit for 21 days, so placing eggs under them is probably a waste of time, but occasionally one will see it through!

Chicken Courtship

Some roosters are a little bit romantic – others not so much. To indicate interest in a particular hen, the rooster will perform the courtship dance.

It’s a bit like a rooster tango – he will approach the hen from the side, dropping a wing near to the ground and do a little fancy footwork around her.

This is his ‘come hither dance, and he will repeat it until she either indicates she likes him or walks away from him.

Hens’ are no easy mark, though – they will have evaluated his merits as a suitor. Does he provide food? Is he a good protector? Is he healthy?

And is he sexy? (a red comb and wattles really get the ladies interested). If he passes the inspection, she will let him mate. If not, she will ignore him.

A Nicely Combed / Wattled Rooster

He will start ‘tid-bitting’ in earnest once spring arrives.

He will pick up interesting morsels for the hen to inspect, luring her over to check it out.

If it turns out to be nothing of interest to the hen, she will brush him off, so he must be on top form in several arenas of showmanship and ability to win her approval.

Occasionally, a hen will dislike the rooster and may never mate with him at all, but this is rather unusual.

Hens also have a neat little trick about rooster sperm.

If they decide they don’t want the sperm from the mating, they can eject most sperm to avoid fertilization.

A Fertilized Chicken Egg: The Mating Process

If you are witnessing a mating for the first time, you can be forgiven for thinking it’s more akin to rape than ‘love,’ but fortunately, the hens don’t see it that way.

The act of mating looks quite barbaric but, in fact, rarely results in serious injuries.
Roosters are very zealous in their mating practices.

He can mate anywhere from 10-30 times per day depending on the level of co-operation from the ladies.

A rooster can adequately cover up to around 15 hens, but in reality, he likely will have favorites that he will tend to more frequently.

The optimum time for mating is early morning, when his sperm load can be anywhere between 100 million – 5 billion sperm!

How does the rooster fertilize the egg?

Once the hen has decided she will accept the rooster, she will squat down to the ground and spread her wings to steady herself.

He will mount her from the back, grabbing her head feathers in his beak and treading her with his feet to find a stable spot on which he can balance.

“The Cloacal Kiss”

What happens next is called the “cloacal kiss”. Inside his cloaca, is a small raised point called the papilla. The papilla is what passes the sperm.

During this “cloacal kiss” the hen must open up her cloaca so his sperm can reach the unborn/unlaid eggs in her oviduct. After he has passed his sperm they carry on their business as usual. The sperm that he passed will fertilize the eggs she had that day and some days after.

He will use his claws to get a steady grip on her – this is where most injuries to hens occur. Her sides can be ripped by claws or longspurs, causing some skin to be torn up.

You can help the hen to ensure that the roosters’ spurs are short and if he is frequently mating with certain hens, fit them out with a hen saddle for protection.

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Chicken Eggs Fertilized

Chicken Reproductive Anatomy


The rooster has two working testes which are located in his abdomen very near to the kidneys.

He can constantly manufacture sperm as needed for mating – ever ready!
The rooster does not, however, have a penis.

He has something called a papilla inside his cloaca. The papilla is a tiny ‘bump’ on the cloacal wall.

The testes deliver the sperm to the papilla via the vas deferens, which, in turn, delivers it to the hens’ cloaca.


A hen is born with two ovaries, but the right one usually atrophies and dies, so the left ovary is the one that will carry all the eggs a hen will ever lay and then some!

The ovary contains hundreds of egg follicles, including the ripening egg. When it is ready to be dispatched, it is dropped into the infundibulum of the oviduct, where it begins its’ descent.

For an in-depth look at chicken reproductive anatomy, see our article.

The Journey

Sperm from the rooster is deposited in the hens’ cloacal area and migrates up into the vagina, where it can rest in ‘pockets’ in the wall.

Rooster sperm is viable for 7-10 days inside the pockets, although fresh is best.

However, sperm intent on fertilizing travel on up into the area of the oviduct known as the infundibulum to ensure success.

The hen’s oviduct is approximately 30 inches long, and the intrepid sperm travels about 29 inches to reach the infundibulum and deliver the genetic code to the germinal disc of the egg.

Once the rooster DNA is delivered to the hen DNA in the germinal disc, they fuse and become a zygote (fertilized seed).

It takes about 5 hours for cell division to start, and at this point, it is called a blastoderm or embryo.
Cell division and expansion continue unabated as the now fertile egg goes through all the stages necessary to make an egg.

This includes laying down albumin, building the shell, and applying the bloom before the eggs lay.

If our hen is interested in being a mother, she will now find herself a nesting place that is quiet and dark.

She will start to cache her eggs until she has enough to start incubating them.
The number in a cache is variable, but you should try to make sure she can cover all the eggs she has 5-8 is a reasonable number.

If she has too many, remove some to another hen or incubator.

Chicken Eggs Fertilized

Development & Brooding

If you allow the hens to hatch their own, you can do a few things to make the process smooth.

Firstly, make sure the rooster can’t hurt her during mating – trim spurs and talons; use a hen saddle if necessary.

Secondly, when she is looking for a dark and secure place to set, try to encourage her into a small separate area where she can be undisturbed by the other birds.

Add in a feeder and waterer, so she has her own little ‘apartment,’ and she should be all set. The area should, of course, be fully secured and be locked down for safety overnight.

Once our hen has decided she has enough eggs to sit on, she will start to brood. This means she will sit on those eggs for the next 21 days until they hatch or die.

She will chase off the rooster if he tries to mate with her at this point.

Once she becomes fully broody, the rooster will not fuss with her. He may be a Mr. Nice Guy and sit on her eggs for a while, but most roosters don’t. His involvement with the chicks will not start until they are hatched.

Our broody will diligently turn, warm, and fuss over her eggs for the next 21 days. During that time, she will rarely leave the nest.

You may see her once a day run out to poop, perhaps have a quick dust bath and then run back to the nest where she will rearrange her eggs before sitting again – total dedication!


Once hatched, Mama will take great care of her little chicks. No one will mess with a broody hen and chicks – she will defend them most vigorously.

They will learn all they need to know from her, and if the rooster is a ‘family guy,’ he, too, will take turns looking out for his offspring.

Here is a complete guide on raising chicks once they have hatched.

Commonly Asked Questions

How do farmers know if a chicken egg is fertilized?

Well the quickest, but most destructive way is to crack the egg open. A fertilized chicken egg has a white spot on the yoke. This spot is called a blastoderm. However, once you have cracked the egg open it is open to bacteria and cannot grow into a chick so it must be thrown out.

Another way to tell if an egg is fertilized is to use candling. Once you have waited a few days for either the mother to incubate the eggs or you have an incubator you can take the egg into a dark room.

When you’re in the room put a flashlight underneath it. If the egg is fertilized it should have a clear spot with veins within the egg.

How does the rooster fertilize the egg?

Neither the rooster nor the hen have genitals meaning no penis or vagina so they have to do something different.

A rooster inseminates a hen with his sperm by jumping on her back, lowering his tail, and touching her cloaca with his.

As we mentioned earlier, this is called the “cloacal kiss”. Inside his cloaca, is a small raised point called the papilla. The papilla is what passes the sperm.

During this “cloacal kiss” the hen must open up her cloaca so his sperm can reach the unborn/unlaid eggs. After he has passed his sperm


The frenetic mating activity of spring and early summer will start to moderate when the days get too hot and humid.

By this time, the broody Mamas will have signed off on their chicks and will soon recommence laying fertilized chicken eggs, and the chicks will be finding their own place in the pecking order.

Any young roosters hatched will generally defer to the head rooster, which helps keep order in the flock.

A rooster is considered old at around 3 years, so if you have an older rooster in your flock, the new boys will be challenging the alpha male at some point.

We hope you have enjoyed this quick trip through egg fertilization. It really is a fascinating and amazing process.

READ NEXT: Hatching Eggs – Everything You Need To Know

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How Are Chicken Eggs Fertilized



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5 thoughts on “How Are Chicken Eggs Fertilized

  1. I have what may seem like a duh question… I have 5 astrulops & 5 Wyandotte and I thought about getting a rooster, but which kind?? A couple of my Wyandotte have exhibited some broodie behavior. Any suggestions would be greatly appreciated. ??

    1. Separate the two types of hen. Get one rooster of each type. It is best to have purebred chickens– both breeds need their own rooster. You can pick up roosters for very little. You can have two houses and a fence between the different groups. Such things are not expensive to create. If the hens will not brood the fertile eggs, an incubator can be used. You may find a used on on line, but at stores or eBay or other websites, they are not expensive.

  2. Since eggs are such a well-loved kind of food, it is no wonder people express some concern about the kind of egg they are eating. One of these concerns is whether the eggs they got from the supermarket are fertilized chicken eggs or not. But wait, aren’t all eggs supposed to be fertilized in the first place? This article aims to clarify just that.

    1. no, there are enough sperm in her system(and the rooster will make sure to replenish), that most likely ALL of her eggs will be fertilized). Once she sits on the eggs, though, and goes broody, she will stop laying eggs altogether until WELL after the chicks are born. My broodies have always waited til the chicks were at least a couple of months old before they’ve started laying eggs again. This is why you will probably want to “break” your hen of her broodiness if you dont want chicks and DO want eggs…cuz she’ll be out of the egg production game for a LONG time. If, on the other hand, you WANT chicks, and have the space/time for them, it’s SO worth the pause in egg production! 🙂

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