Your Chicken Questions Answered by a Veterinarian. Honest and Practical Advice

How Do Chickens Lay Eggs?

“How do chickens lay eggs?” is a common question encountered by anyone who has kept hens without a rooster. It’s easy to laugh, but given chicks do come from eggs, the question isn’t widely off the mark. Also, as more of the global population lives in cities, humans have become less knowledgeable about where and how our food is produced. 

Hens do not need “a man” in their lives to produce eggs. These little orbs of edible gold can be produced unfertilized (no baby chick ever coming out of it) or fertilized (the hen equivalent of being pregnant). But the production of the egg is fascinating.   

Chickens And The Incredible Egg

The majority of eggs consumed are unfertilized (no rooster was involved in your breakfast). Also, it is a myth that fertilized eggs have more protein and higher nutrition. All of this is excellent news for folks raising backyard chickens, as many suburbs have banned roosters due to their noise level (fair).

The reason hens produce eggs is the same reason human females have them: for the potential of reproduction. However, unlike human females who only ovulate once every 28-days, hens have the potential to reproduce regularly. The average chicken cycle is every 24-26 hours, producing 5-6 eggs a week during the season.

Is There A Limit To A Hen’s Egg Production?

Hens cannot produce an infinite number of eggs. Similar to human females being born with all their eggs, hens are born with a finite number of ova, which are the beginnings of the yolk. Thus, even if science found a way to combat aging, a hen’s egg production would eventually cease due to a lack of yolk.

How Do Chickens Lay Eggs: How Does A Chicken’s Ova Become A Yolk?

A hen develops the ova in her ovaries. She only has one working ovary on the left. The second is a spare, much like roosters only use one gonad (think testicle). These “spares” do not develop into fully functioning parts unless the main one is damaged. It is believed that most birds only use one side to keep their bodies lighter for flight.

So back to our ova. When it is an ova’s turn, a follicle in the ovaries begins developing it into a yolk. The ovaries always have a few on the go at different stages. Amongst the yellow yolk is a single “female” cell. The cell is the rooster’s “bullseye,” should there be any baby chicks in a flock’s future.

However, regardless if there is a rooster around to hit the yolk’s target, the golden orb eventually becomes too heavy. At this point, the follicle developing the ova ruptures, and the yolk is released.

How do chickens lay eggs: How Is A Hen’s Yolk Fertilized?

Unlike mammals, birds don’t develop their fetuses in the womb. Many theories have developed around why hens lay eggs, one being that pregnancy is a heavy state and bad for flight. Thus, for a chicken’s egg to have a chance of survival outside its mother, it needs armor, otherwise known as the shell.

Thus, as the yolk detaches from the ovary, it drops into the oviduct. The first part of this chute is called the infundibulum. It is around two inches long, and a yolk spends an average of 15 minutes in this section. It is here, in the infundibulum, that the rooster’s sperm might get lucky. However, given the time restraints, even hens with a rooster hanging around produce unfertilized eggs.

Where Does The White (Albumen) In An Egg Come From?

Once the yolk has done its 15 minutes in the infundibulum, it progresses down the cute into the magnum (you’re never going to look at particular ice cream the same, are you?). The magnum is 13 inches long, and the yolk spends an average of three hours in this section.

It is here in the magnum where the yolk begins to acquire around half of its albumen coating. In simple terms, this is the “egg white.”

How do chickens lay eggs:  here you can see the egg yolks developing

How Does A Chicken Egg Gain Its Shape?

After the magnum is the isthmus. It is only four inches long, and the egg averages 75 minutes here. The isthmus is where the 10% of the albumen membrane is made, giving the egg its shape. 

Do Chickens Have A Uterus?

Although chickens are not carrying their unborn in their womb, they still have a uterus. Also known as the shell gland, this chute section follows the magnum. It is 4.2 inches long, and the egg spends most of its time here, averaging just under 21 hours.

The uterus is where the egg obtains the rest of its album, and its shell is formed, including gaining its pigment.

Once complete, the chicken will lay her egg, passing it through her cloaca, also called her vents or vagina. The final section is only 4 inches long, and the egg spends very little time in this spot. Instead, it is merely a “gateway” for the egg to exit the hen’s body. 

Do Chickens Have Separate Vents For Waste And Laying?

Hens only have one vent, which is used as the exit for eggs and waste. However, waste does not go through the same track as an egg. Eggs are made in the oviduct, the reproductive tube. Chicken waste travels through the intestines.

Also known as the cloaca or vagina, the vent can only perform one task at a time. While an egg is being laid, it is blocking the intestine’s access to the vent. Thus, when there is a bit of chicken poop on an egg, the inside remains clean. This waste was picked up in the final, shared section of the hen’s exit and did not touch the yolk and albumen while its shell was being formed.

Do Chickens Need Sunlight To Lay Eggs?

A hen’s reproductive system is triggered by sunlight or an artificial replica. Most hens require at least 14 hours of daylight to activate their ovary. Older hens probably won’t lay without 16 hours of sunlight.

Can A Double Yolk Egg Create Twins?

A single chicken egg can produce twins. It is rare, and typically both will die before hatching, although occasionally, one pulls through. Unlike a human womb, there is no way for the mother hen to expand the size of the shell or provide extra nutrition to the inside of the egg.

However, in the unlikely event, both chicks were to live, they would not be identical. The double yolk is formed pre-fertilization; thus, each chick is from a separate female cell and male sperm.

Can Chickens Be Identical Twins?

Technically, a fertilized chicken egg could have one yolk where the fertilized cell splits, creating identical twins. However, it is incredibly rare, and as with the case of a double yolk, it is highly unlikely that the chicks will survive long enough to hatch. Nonetheless, saying something is rare is not the same as claiming it is impossible.

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