Many people are curious about how a chicken egg becomes fertilized and develops into a chick. The process of fertilization and embryo development is complex but fascinating In this article, I’ll walk through the step-by-step process of how a chicken egg gets fertilized.
The Male and Female Reproductive Systems
To understand fertilization, we first need to know a bit about the male and female chicken reproductive systems
The Rooster
- The rooster has testes that continuously produce sperm.
- Sperm travels through tubes called vas deferens to the cloaca.
- The cloaca is an opening used for both reproduction and excretion.
The Hen
- The hen has only one functional ovary, on the left side. This ovary holds thousands of ova (undeveloped egg cells).
- The oviduct is a long, twisted tube where eggs are formed.
- Like the rooster, the hen also has a cloaca.
The 5 Stages of Fertilization
Fertilization occurs through the following 5 stages:
1. Mating
- It all starts with mating between a rooster and hen.
- The rooster mounts the hen from behind, grasps her with his feet, and inserts his cloaca against hers.
- He then ejaculates sperm into her cloaca through rhythmic cloacal contractions.
- Mating usually lasts just a few seconds.
2. Sperm Storage
- Sperm travels through the hen’s reproductive tract and is stored in sperm storage tubules located at the junction of the oviduct and cloaca.
- Sperm can be stored here alive for up to 4 weeks.
3. Egg Release
- About 30 minutes after mating, the hen will ovulate and release a yolk from her ovary into the oviduct, ready for fertilization.
- Yolks are ovulated at intervals of about 27 hours.
4. Fertilization
- As the yolk travels down the oviduct, some sperm are released from the sperm storage tubules to meet and penetrate the yolk.
- One sperm fuses with the ovum nucleus to complete fertilization.
- Fertilization happens around 15-17 hours after egg release.
5. Egg Formation
- It takes about 25 hours for the fertilized egg to travel down the oviduct and receive all its components: shells membranes, egg white, shell, and bloom coating.
- The fully formed egg is laid through the cloaca about 26 hours after fertilization.
Developing Embryo
Once the egg is laid, embryo development begins if incubation conditions are right:
- In the first 24 hours, cell division results in a small disc of cells on the yolk surface.
- By day 3, the embryo begins differentiation into distinct areas that will become body parts.
- Eyes, beak, wings, and feet become visible around day 6.
- By day 21, the chick fully forms inside the egg and hatches out.
Fun Facts About Chicken Egg Fertilization
- Hens don’t need a rooster to lay eggs, but they do need one for fertilization.
- One mating results in fertile eggs for up to 2 weeks due to sperm storage.
- Not every egg a hen lays will get fertilized, even with a rooster present.
- There’s no way to tell if an egg is fertile without cracking it open to check.
- Fertilized eggs and non-fertilized eggs look the same and have the same taste.
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!
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 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?
Chickens can lay eggs without a rooster, but those eggs will not be fertilized and therefore will not hatch. Fertilization requires a rooster, who transfers sperm to the hen during mating.
How does a chicken fertilize an egg?
Chicken eggs are fertilized through a process called cloacal contact, where the rooster transfers sperm to the hen via a “cloacal kiss.” This occurs when the rooster mounts the hen, and their cloacas (the common opening for reproductive and digestive tracts) touch, allowing for sperm transfer.
Is it okay to eat fertilized chicken eggs?
Yes, it is perfectly safe to eat fertilized chicken eggs, even if they have been laid by a hen with a rooster. The presence of a germinal disc (the bullseye or white spot on the yolk) simply indicates fertilization, not that the egg is developing into a chick.
Are chicken eggs fertilized?
Most chicken eggs people eat are not fertilized. Most commercial egg farms raise hens without roosters, so the eggs these hens lay have no chance of being fertilized. Fertilized eggs are more common in backyard flocks where roosters are present. So, when you crack open an egg from the grocery store, it’s most likely unfertilized.
How do chickens fertilize eggs?
Chickens — like other birds — lay fertilized eggs via sexual reproduction. Depending on the breed of chicken, a hen will begin laying eggs between five and seven months of age.
How does a rooster fertilize a chicken?
A chicken’s egg is usually fertilized by a rooster when the hen lays the egg. The rooster will mount the hen and pass sperm into her oviduct, which is the tube that connects her ovary to her uterus. The sperm will then travel up the oviduct and meet the egg, which is released from the hen’s ovary.
Do you need a rooster to fertilize chicken eggs?
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!
How does chicken egg fertilization work?
The egg also receives a coating of bloom, which is a thin layer of protein that seals the pores of the shell and prevents bacteria from entering. The egg is finally laid through the cloaca and into a nest or incubator. Watch the chicken egg fertilization process below.
How do chickens lay their eggs?
Chickens are born with all the eggs they will ever lay. The eggs develop in the ovary, and once matured, they travel through the oviduct, where they’re fertilized (if a rooster is present) and then laid. Here’s what that looks like: