Have you ever wondered how chicken eggs get fertilised? It’s a fascinating process that happens inside the hen before the egg even forms its hard shell. Whether you’re curious about backyard chickens, farming, or just love learning about nature, this guide will walk you through the journey of fertilisation in a simple and friendly way.
The Basics: What Does Fertilisation Mean for Chicken Eggs?
Fertilisation is the moment when a rooster’s sperm meets the hen’s egg cell (also called an oocyte), combining their genetic material to create a new life. This union forms a zygote, the very first cell of what can eventually become a chick. But here’s an important fact: the shell you see on an egg doesn’t exist yet during fertilisation. The sperm can only fertilise the egg cell inside the hen’s reproductive tract before the shell forms.
Inside the Hen: Where Fertilisation Happens
A hen’s reproductive tract is about 75 centimeters long and is specially designed to form the egg step by step. Each hen is born with all the egg cells she will ever lay, fertilised or not. Here’s how it works:
– The yolk, which acts as a food source for the embryo if fertilisation occurs, develops in the hen’s ovary.
– When it’s time, the most mature yolk with its attached egg cell is released into a part of the reproductive tract called the infundibulum.
– This infundibulum is where fertilisation can happen – but only if sperm from a rooster is present.
– The sperm must swim approximately 70 centimeters through the hen’s reproductive tract to meet and fertilise the egg cell.
– If the sperm successfully fertilises the egg cell here, the yolk is now fertilised and ready to develop into an embryo.
This fertilisation window is very brief, usually lasting about half an hour before the yolk moves on to the next stages of egg formation.
What Happens After Fertilisation?
Once fertilised, the yolk begins its journey down the oviduct, where it gets covered with layers of egg white (albumen) and membranes. The egg then rotates through a spiral tube, creating chalazae – the twisted strands that hold the yolk centered inside the egg white. Finally, the eggshell forms around the egg, made mostly of calcium carbonate, a mineral similar to limestone or marble.
This entire process takes about 24 to 26 hours. After the egg is laid, the hen can start forming the next egg fairly quickly, often within half an hour.
Can a Hen Lay Fertilised Eggs Without a Rooster?
No. For an egg to be fertilised, the hen must have mated with a rooster. However, hens will lay eggs regardless of whether they have mated or not. If a hen hasn’t mated, the eggs she lays will be unfertilised and won’t develop into chicks.
Interestingly, a hen can store sperm from a rooster for up to two weeks and fertilise multiple eggs from just one mating session. This means one mating can result in several fertilised eggs over days.
How Can You Tell If an Egg is Fertilised?
If you want to check whether an egg is fertilised, there is a technique called candling. This involves holding the egg up to a bright light to see inside:
– Fertilised eggs show a network of fine red blood vessels and a dark spot, which is the developing embryo.
– Unfertilised eggs appear clear inside with no visible blood vessels.
– If an embryo dies during development, the egg will have a large air space that grows as the embryo disintegrates.
Removing non-fertilised or dead eggs from an incubator is important to prevent contamination of healthy eggs.
What Happens to Fertilised Eggs in the Wild or on the Farm?
For a fertilised egg to develop into a chick, it needs to be incubated at a warm temperature, around 37 degrees Celsius (98.6°F), for about 21 days. This incubation can happen naturally when a hen goes “broody” and sits on her eggs to keep them warm, or artificially in an incubator.
Most eggs sold in supermarkets are unfertilised because commercial egg farms usually keep hens without roosters to prevent fertilisation. Even if a fertilised egg makes it to your kitchen, it won’t develop into a chick unless kept warm and incubated properly.
Fun Facts About Chicken Egg Fertilisation
– The eggshell is formed from calcium taken from the hen’s bones, which she replenishes through her diet.
– The eggshell protects the developing embryo from bacteria and parasites.
– The process of shell formation is similar to bone formation but happens much faster.
– Hens can lay an egg every one to two days, depending on breed, age, and season.
Chicken reproduction is a beautifully orchestrated natural process that ensures the continuation of the species while also providing us with the eggs we enjoy every day.
Fertilisation happens inside the hen before the shell forms, requiring a rooster’s sperm to meet the egg cell in the reproductive tract. Without mating, eggs remain unfertilised and won’t develop into chicks. This natural process is quick, complex, and fascinating!