The Egg-Laying Machine: All About the Female Chicken

A female chicken that lays eggs is called a hen. Hens are incredible egg-laying machines, capable of producing over 300 eggs per year. Their specialized reproductive system allows them to churn out egg after egg in orderly clutches. Let’s take a closer look at what makes these egg-laying feathered friends such prolific producers.

Anatomy of a Hen

A hen’s reproductive system is specifically designed for maximum egg production. It consists of two main parts – the ovary and the oviduct:

• Ovary – Located near the backbone, the ovary holds yolks (or ova) in various stages of development. The left ovary is functional while the right one regresses during embryonic development. At hatch, a pullet chick contains thousands of potential ova for future eggs.

• Oviduct – A 25-27 inch long twisted tube where yolks mature into whole eggs as they travel through. It contains five sections:

  • Infundibulum – Surrounds the yolk after ovulation

  • Magnum – Adds thick albumen

  • Isthmus – Forms egg membranes

  • Shell gland – Creates the shell

  • Vagina – Coats the egg with a protective bloom before laying

The Egg Assembly Line

An egg’s creation begins when the ovary releases a yolk into the oviduct in a process called ovulation. From here, the yolk travels through each section of the oviduct, gathering layers along a 24-25 hour journey:

• 0 hrs – Yolk ovulates from ovary into infundibulum

• 025 hrs – Thick albumen added in magnum

• 4 hrs – Membranes formed in isthmus

• 20 hrs – Shell created in shell gland

• 24 hrs – Bloom added in vagina, egg laid

Like a highly efficient assembly line, a new yolk enters the oviduct about 30 minutes after the previous egg is laid. The hen then repeats this cycle almost daily, pausing occasionally to rest between clutches.

Tricking Hens into Constant Laying

In nature, hens only lay eggs in spring. But farmers use controlled lighting to fool hens into thinking it’s spring year-round:

• 10-16 hrs of light daily

• Lights off signals time to roost/rest

• Ovulation decreases dramatically after 3pm, limiting eggs laid later in day

This light manipulation encourages continued ovulation and more frequent egg-laying clutches.

From Pullet to Layer

Pullets (young hens) reach sexual maturity around 16-20 weeks of age. Their first eggs are small as their reproductive systems finalize development.

As pullets transition into mature laying hens, their capacity increases:

• 16 wks – Small first eggs laid

• 20 wks – Sexual maturity reached

• 30 wks – Peak production achieved

• 80 wks – Declining clutch size signals end of prime laying period

A hen’s lifetime laying potential is set at hatch – she can never produce more than the thousands of ova she’s born with. But optimal nutrition and light management enables her to maximize this genetic potential over 12-20 productive months.

When Eggs Go Bad

While hens are impressive egg-producing machines, their systems aren’t perfect. Problems can occur, leading to abnormal egg qualities:

• Double yolks – Two yolks released quickly, makes extra large eggs

• No yolk – Tissue slough causes yolk-less “pullet eggs”

• Blood spots – Ruptured yolk vessels leak blood

• Meat spots – Oviduct wall particles appear as spots in whites

• Shell issues – Calcium deficiency causes weak or missing shells

• Odd shapes – Shell abnormalities cause weird shapes

While odd, most irregular eggs are still perfectly edible. But they can’t be sold commercially, and problematic trends may indicate nutritional issues requiring veterinary attention.

Fun Hen Facts

Below are some surprising tidbits about our fabulous egg-laying friends:

• Hens have a single functional ovary and oviduct, both on the left side. The right versions regress pre-hatch.

• An “egg within an egg” can form when a reversed egg re-enters the oviduct and gets layered again.

• Hens mobilize 10% of their own skeletal calcium to form each egg shell.

• During her lifetime, a hen uses over 2 pounds of calcium just for her eggshells.

• The world record for eggs laid by a single hen is 371 in 364 days!

• Champion layers can produce over 50 lbs of eggs annually.

• Light stimulates ovulation and egg production. Heaviest laying occurs in spring.

• Given proper feed and lighting, hens naturally lay about 1 egg every 1-2 days.

In Summary

When we see a chicken lay an egg, it looks simple. But within that hen, a remarkable 25-hour process of female reproductive anatomy has swiftly and efficiently transformed a yolk into a complete, shelled egg. The hen’s ovary and oviduct work together in perfect synchronization, churning out egg after egg in a continuous laying cycle. With her specialized equipment, a healthy, well-managed hen can lay up to one egg per day for much of her life – an incredible feat of animal agriculture!