How Chickens Make Eggs and 3 Common Egg Laying Problems

How Chickens Make Eggs and 3 Common Egg Laying Problems Blog Cover

An egg contains a phenomenal amount of nutrition for its size, but you already knew that right?

An average egg contains a mere 75 calories but gives you 7g protein, 5g fat and 1.5g of saturated fat. In addition it gives you vitamins A, D, B12, riboflavin, pantothenic acid, phosphorus, choline, carotenoids and cholesterol!

And as reported by Pennsylvania State University if you eat only pasture raised chicken eggs instead of generic supermarket eggs, you get even more health benefits- making it truly a superfood.

We’ve previously talked about why your hen has stopped laying and also, the best chicken breeds for lots of eggs, but we haven’t discussed where does this incredible food come from? To just say it comes from a chicken doesn’t do justice as to how complex the process is.

After reading this article today you will realize what a small miracle that egg really is.

The Reproductive System of the Hen

A hen is born with two ovaries.

Although after a chick has hatched their right ovary shrinks, becoming non-functioning, so all the egg laying activity is located in their left ovary.

Interestingly, all the eggs a hen will ever lay are stored in their ovary at birth.

The egg machinery (i.e. oviduct) of the hen is about 25-27 inches long. It really looks like a stretched out trumpet. Let’s take a look at each part of the oviduct and how it works together to produce an egg.

Chicken Oviduct
Photo Source: University of Kentucky College of Agriculture

Step 1: Follicle

It all starts in the Follicle; a mature yolk is released from the follicle into the infundibulum. The follicle contains all of the yolks a hen will ever lay in her life; she likely will not use all of them. The release of the yolk stimulates hormonal responses throughout the system.

Step 2: Infundibulum

The yolk spends about fifteen minutes in the infundibulum, where it is gently ‘massaged’ and stretched out. If fertilization is going to occur, it happens here.

Step 3: Magnum

Once the yolk leaves the Infundibulum, it passes through to the Magnum. This is the largest part of the reproductive system where approximately 50% of the thick, white albumin is attached. The yolk remains here for about three hours before moving on.

Step 4: Isthmus

After the yolk has passed through the Magnum, it reaches the Isthmus. The shape of the egg is determined here and the inner and outer shell membranes are attached.

Step 5: Uterus

Once the shape has formed the egg passes through to the Uterus (shell gland).

Here the egg shell is made. The shell is largely made from calcium carbonate. The hen pulls roughly half the calcium from her body and the other half is obtained from her diet. If there is any pigment to be added to the egg, this is where it happens. The egg remains in the uterus for around twenty hours.

This is commonly an area where things go awry in the hens’ ability to maintain a good production egg.

Step 6: Vagina

Not really important to formation, the vagina is all important in getting the egg laid properly. The ‘bloom’ of the egg is laid down here and the egg is turned in a process called ‘oviposition’. The egg enters the vagina narrow end first, but is laid ‘blunt’ end first.

Occasionally, an egg will get ‘stuck’ while turning around- this is called egg bound.

The hen can sometimes expel them herself, but on occasion may need assistance from her keeper.

‘Sperm pockets’ are located in the walls of the vagina. During fertilization, some sperm is released and travels up to the infundibulum for the process to begin. Bird sperm remains viable at body temperature for 10-14 days.

Step 7: Cloaca

Finally the egg reaches the Cloaca which is the Thruway exit!

The entire process takes around 25-27 hours, so you average hen will lay slightly less than an egg a day- this is an average of around 270 eggs per year for a hen in their first year of lay!

Once an egg has been laid, within thirty or so minutes another will start on its own journey.

It is rare for a hen to start ovulation after 3pm, so once every 6-7 days she will miss a day of production.

Overview of Egg Laying Process

Overview of Egg Laying Process

The Anatomy of the Egg

The egg consists of many separate pieces, all nicely packaged up to give you breakfast!

Egg Anatomy Diagram
Anatomy of an egg by Frank Horst
  • Eggshell: This holds everything together. The shell consists almost entirely of calcium carbonate and is perforated by up to 17,000 pores to allow passage of air and moisture between the egg and the air.
  • Outer shell membrane
  • Inner shell membrane: These membranes sit side by side just under the shell and act as defense mechanisms against bacteria.
  • Chalaza: The stringy bits you hate! They are attached to the yolk, twisted in opposite directions and serve to keep the yolk centered. This is vitally important for the correct development of a chick.
  • Exterior albumin: Thin outer layer of albumin next to the shell membrane.
  • Middle albumin: Thicker, white albumin. It is a good source of riboflavin and protein.
  • Vitteline layer: The clear casing that the yolk is wrapped in. The integrity of the vitteline layer is important to prevent ‘splotching’ on the yolk.
  • Germinal disk: This is a 2-3mm white spot on the yolk surface. This is where the sperm enters the egg. The embryo will develop from this disk.
  • Yellow yolk: This is the essence of life, if you will. It contains all the nutrition an embryo will need to become a chick.
  • Air cell: When the egg cools, an air space forms. During aging, moisture and carbon dioxide leave through the pores of the shell and the air cell enlarges. This is why an old egg will float.
  • Cuticle/bloom: This is an outer coating, placed whilst the egg is in the vagina. It seals the shell, preventing bacteria from going in and moisture from coming out.

Three Most Common Egg Laying Problems

Soft Shell or No Shell Eggs

This is caused by a malfunction in the uterus. It may simply be that the pullets’ reproductive equipment is too immature yet and requires a slightly longer development time. Or it could be that the hen is aging or it’s simply a genetic ‘oops’.

Malformed Chicken Shell
Parchment Shell

I have one thirty month old hen who consistently lays ‘shell troubled’ eggs. The pictures below show a parchment shell removed from the vent and an irregular coating of shell. She fairly frequently lays no shells and sometimes a perfect egg!

Although she is currently well, she is in danger of egg yolk peritonitis from one of these episodes.

Egg Yolk Peritonitis

This occurs when fluid from the oviduct leaks into the abdominal cavity and starts an infection. The yolk is a superb place for E. coli bacteria (from the gut) to grow in and the hen will get sick quickly and often dies almost before you notice she is sick.

Unfortunately, many diagnoses of egg yolk peritonitis are made at autopsy.

Egg Binding

Normally, when the egg travels into the vagina it turns itself around so that it is laid blunt end first. Sometimes if it is too large, it will get stuck, causing the hen to be ‘egg bound’.

If this happens the egg needs removing or you hen can become very ill.

A warm water bath and some gentle massage of the abdomen can help. You can also lubricate the vent with some Vaseline to assist in the passage of the egg.

If the process goes well you should end up with some beautiful eggs, like these!

Chicken Eggs

So there you have- the miracle of the egg. A little power house of nutrition carefully packaged by the hen. Did you know that eggs were so complex!?



Comments

  1. Olga Bryant says

    I have 4 approx 8 month old hens, one by one they started laying, the last one just 7/8 days ago.
    But we have just had a soft shell egg, and the yolk laying next to it not inside the shell. I’m assuming it is probably the last hen to start laying, should I be doing anything to help.

    • The Happy Chicken Coop says

      Hi Olga,

      As mentioned in the article, when pullets start to lay you do get some weird and wonderful types of eggs.

      However, with the shell problem I would suggest feeding them crushed oyster shell to see if this fixes it.

      Claire

    • The Happy Chicken Coop says

      How old is your hen Elisa? It’s normal for point of lay pullets and young hens to lay small eggs whilst they are still developing.

      Claire

  2. Carolyn Weibye says

    Problem with one yr old approx.laying eggs. It takes her over 3 hours with great distress. She makes loud calls every time she bears down. I gave her the warm bath/massage 2 days ago and it seamed to ease her. Her vent seams large enough. She finally laid a perfect egg. I can not be here every day to do this. Is the problem that the egg is not turning around in the vagina? What can I do?

    • The Happy Chicken Coop says

      Hi Carolyn,

      It sounds to me like Egg Binding. I’m writing an article on this soon to explain what it is and how to treat it. In the meantime, head over to YouTube as there are several good videos explaining this.

      Email me if you need any help,

      Claire

  3. peggy says

    We have had 3 chickens for 1 1/2 yrs. Black Sexlink. About Sept. one of them stopped laying. we waited thinking she began molt early but alas here it is March and the others are laying nearly each day but not one of them.
    We don’t know ‘who’ is the hold out. but i noticed today that one of the hens is smaller and her comb is not bright and fresh like the other two.

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