As a backyard chicken owner I often get questions from curious folks about how roosters fertilize eggs. It’s a fair question if you’re new to raising chickens! I’ll explain the process in simple terms in this article.
A Quick Intro to Chicken Reproduction
First let’s review some chicken biology basics. Hens are female chickens and roosters are male chickens. Hens have ovaries and oviducts where yolks and egg whites develop, and finally eggs are laid. Roosters have testes that produce sperm.
For an egg to become fertilized and develop into a chick, the sperm from a rooster must join with the egg yolk inside the hen’s oviduct.
How Mating Occurs
The fertilization process starts with mating. When a rooster mates with a hen here’s what happens
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The rooster will mount the hen and rest his chest on her back while flapping his wings to maintain balance.
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Their cloacae (vent openings) make contact. The rooster’s cloaca releases sperm, which travels into the hen’s cloaca.
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The sperm then travels up to the hen’s oviduct, where it can survive for 2-3 weeks.
So essentially, the physical act of mating allows the rooster to transfer his sperm from his cloaca to the hen’s. The sperm gets stored internally and can fertilize eggs during the next couple of weeks.
When Fertilization Happens
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As a yolk travels down the hen’s oviduct over 24-26 hours, it may encounter live sperm stored from a prior mating.
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If sperm penetrates the yolk, fertilization occurs. The germinal disc on the yolk begins dividing into a cluster of cells that will become the embryo.
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The egg white forms around the yolk as it travels through the oviduct. Eggshell membranes are added in the uterus.
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Finally, the shell forms in the shell gland. At this point the egg is fully formed, and is laid through the cloaca 20-26 hours after the yolk’s release.
Signs of a Fertilized Egg
How can you tell if an egg is fertilized? Here are a few ways:
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Candling: Shine a bright light through the egg in a dark room. Fertilized eggs will show a dark spot and a network of veins from embryo development.
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Crack it open: Look for a white spot on the yolk called the blastoderm or germinal disc. This is where the embryo starts to grow.
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Float test: Fertilized eggs tend to lie flat on the bottom when placed in water. Unfertilized eggs are more buoyant.
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Incubate it: If you incubate an egg for several days and don’t see embryonic development, it’s unfertilized.
Do Hens Need Roosters to Lay Eggs?
Here’s an important fact: hens can lay eggs just fine without a rooster around! The egg-laying process is automatic for hens that get adequate nutrition and daylight.
However, the eggs won’t be fertilized or hatch into chicks without a rooster’s contribution. Basically, roosters are necessary for fertilization but not for basic egg production.
In Summary
In chickens, fertilization occurs when sperm from the rooster penetrates the yolk inside the hen’s oviduct. This happens after mating, when the rooster transfers sperm into the hen’s cloaca where it’s stored. As yolks develop into eggs over 24-26 hours, some may encounter sperm and get fertilized. We can identify fertilized eggs by candling, cracking them open, floating tests, or incubating them to check for embryos. And hens don’t need a rooster simply to lay unfertilized eggs.
Do Fertilized Eggs Look Different?
Fertilized eggs do not look obviously different upon first examining them. Without cracking the egg, you can shine a light into the egg and see spider veins and a dark area if the embryo has started to develop. An egg that hasn’t been fertilized will look translucent.
When comparing the yolks inside of the eggs (after cracking them open), you can look for the germ spot. The germ spot is a white circle just outside of the center of the yolk. A fertile egg will have a larger white spot with a clear space in the center. An infertile egg will have a smaller white spot. This can be hard to identify if you aren’t comparing a fertile yolk with an infertile yolk.
How Fertilized Eggs Develop Into Chicks
After a fertilized egg is laid, it will only develop into a chick if it’s kept warm. Depending on a lot of factors (we will talk about this soon), a hen doesn’t always have the desire to incubate the eggs. It’s a big job! She will sit on the eggs for the majority of the day to keep them warm.
Incubating the chicken eggs yourself is a 21-day process that involves keeping the eggs at a certain temperature and humidity level, as well as turning the eggs!
After a week of incubating you can shine a light and see the veins and embryos forming as we previously mentioned.
If fertilized eggs aren’t incubated they won’t develop into chicks. A hen will look for a comfortable stress-free place to lay her eggs and incubate them. Nesting Pads are a great addition to the chicken coop.
How do chicken eggs get fertilized? *More Than You Ever Wanted To Know*
FAQ
How does a male chicken fertilize an egg?
Are rooster eggs good to eat?
The eggs may have a blood spot in them if the hen and rooster have mated, but they are still edible and taste the same.
How many times a day does a rooster mate?
Are hens happier with or without a rooster?
In general though, most hens are perfectly happy WITHOUT a rooster present, especially if kept contained. Some roosters make good sentries, so if free ranging days, can warn of predators, which may help some free ranged hens feel safer???