Hens don’t need a rooster to lay eggs, but they do need a rooster in order to lay fertilized eggs. Chickens are different from mammals in a lot of ways when it comes to their anatomy and therefore their reproductive system. Let’s talk about how eggs are fertilized by chickens.
When roosters mate with hens, they transfer their sperm through cloacal contact and not by penetration. The first fertile egg is laid between 36-48 hours after mating. So an egg laid the day the chickens mate won’t be fertile and an egg laid three days later is fertile.
Chicken egg fertilization is a fascinating process that results in the creation of a new life. For many backyard chicken keepers, witnessing this miracle of nature is an incredibly rewarding experience. In this article, I’ll walk you through the step-by-step process of how a rooster fertilizes a hen’s eggs.
An Overview of Chicken Egg Fertilization
When sperm from a rooster combines with an egg from a hen, fertilization takes place. The resulting cell, called a zygote, has genetic material from both parents. Once fertilized, the zygote divides and grows into an embryo inside the egg.
For fertilization to happen, a rooster and hen must mate. Hens are able to store sperm for up to 4 weeks after mating. They can then continue laying fertilized eggs during this time without the need for additional matings.
It takes approximately 26 hours for a fertilized egg to develop and be laid. Out of all successfully mated hens, only around 60% of their eggs will be fertile.
Now, let’s take a closer look at each step of the fertilization process.
Step 1: Mating and Insemination
Mating begins when a rooster approaches and courts a hen. He will circle around her bob his head and drop one wing in a dance-like display. If the hen crouches down, it signals her acceptance of his advance.
Rooster stands on the hen’s back and wraps his wings around her to get on top of her. Then he presses his cloaca against the hen’s cloaca. The cloaca is an opening that connects the reproductive, digestive, and urinary tracts. In this way, his sperm can go straight into her oviduct.
Once inseminated, sperm can survive inside the hen for 4-6 weeks. The sperm makes its way upward to be stored in tiny glands near where the oviduct meets the ovaries. Here, the sperm lies in wait for an egg to be released.
Step 2: Egg Release
No matter if a hen has mated or not, every 24 to 26 hours, her ovaries will release one yolk on their own. This process is regulated by daylight stimulation.
As the yolk is released, it’s grabbed by the infundibulum (funnel-shaped part of the oviduct). The yolk then begins its journey down through the oviduct where fertilization and egg development occurs.
Step 3: Fertilization
If sperm is stored inside the hen’s oviduct, some will migrate up to the infundibulum to meet the descending yolk. The sperm penetrates the yolk’s membrane and one sperm fuses with the egg nucleus.
This joining together makes a zygote, which is the very first cell of a possible chick embryo and has genes from both parents. The zygote begins multiplying into more cells almost immediately.
Fertilization typically happens within 15-30 minutes of the yolk’s release into the oviduct.
Step 4: Egg Development
Once fertilized, cell division continues rapidly as the zygote travels down the oviduct. After about 4-6 hours, there are between 4,000-60,000 cells present.
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In the magnum portion of the oviduct, albumen (egg white) is added around the multiplying cells. Albumen provides hydration, nutrition and cushioning.
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In the isthmus, shell membranes are added. These provide protective barriers around the yolk and white.
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Lastly, the shell gland adds the hard calcium carbonate shell. The bloom, a natural coating, is added at the very end to seal pores.
The complete egg is laid through the cloaca after around 25-26 hours from fertilization. The hen will then start the cycle again, releasing a new yolk shortly after.
Step 5: Egg Laying
Once fully formed, the fertilized egg is pushed down and out of the hen’s cloaca. It emerges blunt end first.
The hen may make distinctive clucking sounds during the laying process. Some hens also do a “victory lap” around the coop afterwards.
From the outside, freshly laid fertilized eggs look identical to unfertilized eggs. There is no way to know if an egg contains a growing embryo without cracking it open.
Fun Facts About Chicken Egg Fertilization
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On average, only 60% of a hen’s eggs will be fertile after a successful mating.
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Sperm can survive for up to 4 weeks inside a hen before fertilizing an egg.
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It takes a fertilized egg roughly 26 hours to fully form and be laid.
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Blood spots sometimes seen on an egg yolk have nothing to do with fertility. They are simply ruptured blood vessels.
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Store bought eggs are never fertilized since commercial hens are kept separate from roosters.
An Amazing Process!
What is The Cloaca?
A hen has just one opening where both feces and eggs exit the body. This is also where sperm enters. The rooster’s cloaca passes feces and transfers sperm to the hen.
Chickens don’t urinate! They don’t have bladders or urethras, liquids exit with their poop through the cloaca. Since they don’t produce liquid urine their chicken coop is able to stay dry much easier than if they were soiling their bedding all day. Their liquid feces are able to dry quickly.
When the hen and rooster make cloacal contact, sperm enter the oviduct and are stored in glands that can store over half a million sperm. Sperm can stay alive in the storage glands for up to 3 weeks fertilizing eggs. An egg is fertilized about 24 hours before it’s laid.
How eggs are fertilized by chickens is more similar to mammals than you might think. Considering the fertilizing happens inside of their body even though the growing happens outside of their body!.
What Mating Looks Like
Before a rooster mates with a hen he will prance around her and cluck. When he mounts the hen, he bends his tail down and the hen will lift her tail up. The cloaca vents will press together and the rooster injects his sperm.
How do chicken eggs get fertilized? *More Than You Ever Wanted To Know*
FAQ
How do farmers know if a chicken egg is fertilized?
Farmers can determine if a chicken egg is fertilized through candling or by cracking the egg open and observing the yolk. Candling involves shining a bright light through the egg in a dark room to see if there are signs of development, such as blood vessels or a dark spot (the embryo).
How do chicken eggs get fertilized without a rooster?
If a chicken doesn’t have a rooster, it can still lay eggs, but those eggs won’t be fertilized, so they won’t hatch. Fertilization requires a rooster, who transfers sperm to the hen during mating.
How does the chicken egg get fertilized?
Chicken eggs are fertilized through a process called the cloacal kiss, where the rooster transfers sperm to the hen’s cloaca during mating. This sperm then travels to the oviduct, where it can fertilize the yolk as it passes through.
Why do hens lay unfertilized eggs?
Hens lay unfertilized eggs because they are naturally designed to do so as part of their reproductive cycle. The egg-laying process is triggered by hormonal changes, and a hen will lay an egg whether or not a rooster is present to fertilize it.