Knowing how a hen produces eggs helps us recognize and manage potential reproductive issues. Young and old hens can experience laying problems such as shell-less eggs, egg binding, or double-yolked eggs. This article explains the reproductive system of a female chicken and how both table eggs (edible eggs) and fertilized eggs (which hatch into chicks) are formed. Understanding this process can help chicken owners take better care of their birds.
The Hen’s Ovary: Where Egg Formation Begins
Unlike most animals that have two ovaries, hens have only one functional ovary—the left ovary. This adaptation likely helps birds stay lightweight for flight. The ovary contains many small sacs, similar to a bunch of grapes, each holding an undeveloped yolk.
Once a hen reaches maturity at around 18–20 weeks of age, some yolks begin to grow. When a yolk reaches the right size, it is released from the ovary and enters the oviduct, where the rest of the egg formation process takes place.
The Journey of a Table Egg
Step 1: Ovulation and Pickup by the Infundibulum
When a yolk is released, it enters the infundibulum (or funnel), the first part of the oviduct. This section holds the yolk for about 15 minutes.
Step 2: Albumen (Egg White) Formation in the Magnum
The yolk then moves to the magnum, where the egg white (albumen) forms around it. This process takes approximately 3 hours.
Step 3: Membrane Formation in the Isthmus
Next, the egg enters the isthmus, where the inner and outer shell membranes develop. This step lasts about an hour.
Step 4: Shell Formation in the Shell Gland (Uterus)
The egg then moves to the shell gland (also known as the uterus), where the shell forms. This process takes about 20 hours and uses up to 10% of the hen’s total calcium reserves. The shell gland is also where pigment is added to the shell, determining the egg’s color (e.g., white, brown, or blue).
Step 5: Final Touches in the Vagina
The egg moves into the vagina, where it gets a protective coating called the “bloom” or cuticle, which helps prevent bacterial infections. The vagina also positions the egg so that it is laid cleanly without contamination from fecal matter.
How a Fertilized Egg Is Formed
For an egg to be fertilized, a hen needs to mate with a rooster. The mating process is quick, lasting only a few seconds. The rooster transfers sperm to the hen’s cloaca, where it travels to the infundibulum.
Since the yolk stays in the infundibulum for only 15 minutes, hens have specialized sperm storage glands that can keep sperm alive for up to two weeks. This allows fertilization to occur even if sperm was stored before a yolk was present.
Once fertilized, the egg follows the same journey as a table egg. However, after being laid, it will not start developing into a chick unless it is kept under the right temperature and humidity conditions—either by a brooding hen or in an incubator.
Common Egg-Laying Problems in Hens
1. Shell-Less Eggs
Sometimes, hens lay eggs without shells. This could be caused by:
- A lack of calcium in their diet
- Stress
- Illnesses such as Infectious Bronchitis
- The hen’s age (young hens or older hens are more prone)
2. Egg Binding
Egg binding occurs when a hen is unable to lay an egg. This can be life-threatening and requires immediate intervention. It is often caused by:
- A lack of calcium
- Poor nutrition
- Stress or cold weather
3. Egg Yolk Peritonitis (EYP)
EYP happens when the yolk misses the infundibulum and ends up in the abdomen. This can lead to infection, which is often fatal. The best way to prevent EYP is by ensuring proper nutrition and care for the hen.
Understanding how a hen’s reproductive system works helps poultry owners ensure the health and well-being of their birds. Providing a balanced diet rich in calcium, maintaining hygiene, and reducing stress can prevent many reproductive problems. By taking good care of their hens, owners can ensure a steady supply of healthy eggs, whether for consumption or hatching.
FAQ’s
Q1: How does a hen produce eggs?
Hens have a single functional ovary that releases yolks, which travel through the oviduct. Along the way, the yolk gets coated with egg white, membranes, and a shell before being laid. The entire process takes about 24–26 hours.
Q2: Do hens need a rooster to lay eggs?
No, hens can lay eggs without a rooster. However, the eggs will not be fertilized and cannot develop into chicks without a rooster.
Q3: What is the purpose of the bloom or cuticle on an egg?
The bloom, applied in the vagina, is a protective coating that prevents bacteria from entering the egg and helps maintain freshness.
Q4: How can I tell if an egg is fertilized?
Fertilized eggs can be identified by candling after six days of incubation. Look for a spider web-like pattern of blood vessels inside the egg, indicating embryo development.
