How eggs are made

I recently had a question posed to me by someone who is starting out with a backyard flock.  His hens laid an egg each on the first day, but it has been several days now, and nothing.  What’s up?  He describes his coop, and I get the impression that he is doing everything right, but still no eggs. 

To answer his question, I started describing how eggs develop in the hen, and then thought…..others might want to see this….so, for Andrew, and the rest of you….here is how an egg is made:

The yolks are made in the ovary of the hen.   They are stimulated to grow by a hormone cascade that is started by the hen sensing an increasing day length.  As long as the hen is old enough to be sexually mature and has the nutrition and health to allow her to build the yolks, they are all but inevitable.  For Andrew’s question, I would suggest he give the birds an increase in day length….maybe 15 minutes every week for a couple weeks.  There is another factor though…..

A drawing of an ovary with developing yolks....notice how many are developing

It takes 5-6 days for an ovum to grow into a yolk and be released.  Now…if a hen is stressed (by moving homes, illness, etc, etc), and she goes “out of lay”, she will need to re-start that process of yolk growth.  If she is ready to begin again immediately, it will take 6 days before she lays again (5 days of yolk growth, and 1 day for the rest of the egg to be produced).  If she takes a couple of days before she feels good again, it will take 6 days from then.  In professional barns, even with pretty much ideal handling and preparation, most pullets don’t start laying until the middle to the end of the week after they get into the laying barn.

This is the real thing...the pink bulge under the ovary is an egg with white around it in the shell gland, starting to get the shell added.

This “reset” is not uncommon.  It will also happen if the birds have a health setback, feed or water interruption or have decreasing day length.  This is different than the bird taking a day off.  Hens develop a group of eggs at a time.  The number of eggs in this “clutch” is variable, and the more the bird has been selected for egg production, the longer she goes before reaching the end of her clutch.  After the clutch is done, the hen takes 1 or 2 days off until the next yolk is ready to become an egg.  The clutch started off as the number of eggs a hen would lay each year….ie she would lay an egg a day until she had the nest full (5-7 eggs), then stop and sit on em until they hatched.  Now, clutches can be as long as 100 eggs without taking a day off.

So….basically….if a hen gets “bumped” out of production for any reason, it will take her a minimum of 5-7 days to start back to laying eggs.  If she is “in lay”, she may take the odd day off.  In order to stimulate a flock to lay eggs, keep the day length increasing, and don’t let it decrease.  Beyond that, the hens will do the work, once they are comfortable and settled in.

Mike the Chicken Vet

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10 responses to “How eggs are made

  1. Interesting that it takes 6 days. If you keeps purebreeds you usually won’t get an egg a day consistently, so I assume you are talking about commercial hybrids here. I get good laying performance out of my anconas, but only in laying season. I also keep standard sussex and wyandottes and they are reasonable layers although won’t give an egg a day usually, although it can depend how old they are.

    In the case of broody chickens, what influences the time taken for them to come back into lay? I have found that it’s often about six weeks which coincides with when the chicks are fully feathered and can be independent. Is it hormonal?

    • Let me preface this answer with some transparency….I am primarily a vet for professional egg farmers, who use commercial hens. I am not an expert in fancy or traditional breeds. There are a lot of commonalities that should hold true for both though. In the case of broody hens, what happens is that they completely go out of lay. They have the physiology of pullets again. Thus, when they are ready to start coming into lay again, they have to begin the whole hormonal cascade again. This takes around 4-5 weeks in commercial strains, and it will likely be similar for wyandottes and anconas. This means that the pineal gland must stimulate the hypothallamus, which then stimulates the pituitary, which then stimulates the ovary, which then begins to start making yolks. This is different from a hen who goes out of production due to stress…..all she needs to do is let the ovary kick back in….the rest of the machinery is already up and running….hence the 5 days vs the 5 weeks. Hope this helps clarify….I didn’t want to get too convoluted in the main post, as people’s eyes tend to glass over… 😉

      Mike the Chicken Vet

  2. Hi Mike!

    This helps so much! I did a ton of research but did not know about the “reset”. You put the blog post in the perfect level of diction, and me, a non chicken expert found it very easy to understand!

    I just wanted to make sure that I was not doing anything wrong.

    I will keep the day length increasing by 15 minutes / week, and will be sure that the length never decreases.

    I love reading your post. This helps a lot.

    Thanks for all you continuing help and support,

    Andrew

    • One thing Andrew….don’t lengthen your daylenght beyond about 15 to 15.5 hours…whatever you have to go to to get them to lay….too long a day length is stressful too….the girls need time to sleep and rest too. That wasn’t clear in the post, and I didn’t want to lead you astray.

      Mike

  3. Thanks for the clarification Mike. Your post is very informative.

  4. Hi Mike,

    I have been making sure that the chicken’s feed bowls has been full for the whole day, and then at night I put it away.

    Should I only be putting a certain amount of feed in the bowl during the day, or should I just make sure that their bowl is full all the time during the day?

    How much should I be feeding them?

    I appreciate the time you put into replying to comments, and making new posts!

    Andrew

    • For the most part, I would suggest that backyard flocks should be fed ad-lib….always keep feed available for them. In professional farms, the amount of feed is more controlled, and averages around 100-115 grams per bird per day, but since backyard flocks have to deal with larger swings in temperature, less precise nutrition, and more variable surroundings, let them eat as much as they want, and they will usually eat pretty close to what they need.

      Mike

  5. Hi there, constantly i used to check website posts here early in
    the daylight, for the reason that i like to gain knowledge of more and more.

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