Backyard Poultry

How Often Do Chickens Lay Eggs? and How Do Chickens Make Eggs?

Flock Management : Layer Nutrition

Flock Management : Egg Production

Patrick Biggs, Ph.D.

Nutritionist, Companion Animal Technical Solutions

Laying hens lay up to one egg per day at their peak. This is because the egg formation process takes 24-26 hours per egg. Eggs are formed from the inside out, starting with the egg yolk egg white and egg shape. The biggest part of the process is forming the egg shell which takes 20 hours and requires 4 grams of egg shell calcium.

Most flock raisers will tell you there’s something special about walking to the backyard and grabbing a few eggs for breakfast. In the ‘pets with benefits’ equation, farm fresh eggs are protein-packed gifts that families across the country have come to love. 
Infographic showing how chicken eggs are formed through a 24-26-hour processBut how often do chickens lay eggs? And just how to chickens make eggs? The magic behind each farm fresh egg is a 24-26-hour process, with much of the work happening overnight. At their peak, laying hens can lay up to one egg per day.

The biggest involvement for the laying hen is creating the egg shell. The shell defends the yolk from harmful bacteria and keeps the chick or yolk safe. Hens spend much of the egg formation process making sure the calcium-rich shell is strong and protective. When the lights are off and the hens are sleeping, that’s when most of this internal work happens.
The fact that shells are created at night is clear when looking at the egg formation timeline. For example, if a hen started the process at 7 a.m., she would create the egg shell starting around 12 p.m. and continue for 20 hours during the evening and through the night.
Hens are sleeping at night and not eating, which is why both large particle and small particle calcium are important. Through the entire egg formation process, hens incorporate nutrients from their feed into the egg and shell. Purina® complete layer feeds with the Oyster Strong® System include both forms of calcium so hens get the nutrients they need during the full process.

How do chickens lay eggs? Here is an approximate outline of the egg formation timeline:

Yolk release (1/2 hour):

Each female chick is born with thousands of immature yolks, known as chicken ova. For most chickens, the ova begin to develop into yolks when the hen reaches 18 weeks old. Once a yolk has been selected to develop, it spends the next 10 days growing in size. When it is time for the yolk to be released, it breaks out of its protective membrane and drops into the infundibulum or the beginning of the oviduct. This release takes about half an hour.

Initial egg white is created (3 hours):

As the egg enters the hen’s reproductive tract, the egg white begins formation, starting with a clear, protective yolk casing called the vitelline membrane. As the yolk enters the magnum, layers of thick and thin proteins, known as the albumen, create the egg white.  As the contents travel down the oviduct, they spin. This spinning motion causes the formation of the chalazae or the white, stringy pieces you see in an egg. The chalazae’s role is to keep the egg yolk in the center of the egg instead of sticking to the shell. 

Egg shape is formed (1 hour):

Just before the egg enters the shell gland, it spends an hour in the isthmus. While there, the inner and outer shell membranes are added around the albumen and the contents begin to take on the oval shape you expect.

Egg shells are formed, built primarily of egg shell calcium (20 hours):

The most significant piece of the egg formation process happens in the uterus or ‘shell gland’ of the hen. The developing egg spends about 20 hours in the shell gland, where the shell is formed and egg shell color is added during the last 5 hours.

The shell formation takes the most amount of time to complete.  It is important that the hen is fed a diet that contains the proper nutrition, so that she has the nutrients she needs to make the egg shell as strong as possible.  A solid shell is the best defense against bacteria that will try to get inside the egg.

Egg shell formation requires about 4 grams of calcium per shell; 2 grams of which must come from the hen’s diet. If the hen does not have enough dietary calcium to support shell production, she will get the needed calcium from her specialized (medullary) bones.

To help laying hens lay strong and stay strong, select a complete chicken layer feed that includes the Oyster Strong® System. The Oyster Strong® System contains oyster shell along with added vitamin D and manganese to provide a source of calcium that is released over time to supply calcium to hens at night, when they need it most.
In breeds that lay colored eggs, pigments, called porphyrins, are secreted from cells within the uterus to add color to the egg shells during the last 5 hours of shell formation. Blue egg layers add pigment early in the shell formation process, which is why these shells are blue all the way through. A combination of blue and brown pigments produces a green shell color, as with an Olive Egger. Hens that lay white eggs do not produce any pigments during shell formation.

Egg bloom is added and egg emerges (seconds):

The formed egg travels to the vaginal area where egg bloom is added to the shell as the egg passes through. Egg bloom, or the cuticle, is a protective coating that works with strong shells to protect the egg from bacteria. A natural lubricant is also added to the shell for a safe exit through the cloaca.

About 30 minutes after laying an egg, the next yolk will be released from the ovary and the process will repeat itself until she has laid 8 to 12 eggs. After that, she will take a day off from egg production and will start laying eggs again. To help the process go smoothly and to keep hens healthy and productive, always provide your hens a complete layer feed. After all, the formation of nutritious eggs is contingent on what the birds eat.
Give your hens everything they need with a Purina® complete layer feed. Sign up for the Feed Greatness® Challenge.*

*The Feed Greatness® Challenge is a 60-day feeding trial where you will feed Purina® feed, monitor your flock's performance and health, take pictures and receive emails with helpful information.