Why do chickens continuously lay unfertilized eggs?

Why do chickens continuously lay unfertilized eggs?

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As per subject: why do chickens continuously lay eggs even if they are not fertilized?

Is this sort of behaviour found in other species of birds (or other egg-laying animals), or only in chickens? Is it natural, or domestic chickens have been specifically bred for it?

If it's natural, what kind of sense does it make to divert energies and nutrients to continuous lay unfertilized eggs which have no purpose other than being possibly eaten by someone else? How could such a wasteful reproductive behaviour have evolved? Even if it has been specifically selected for in breeding, it still seems to make very little sense in the first place.

Chickens are domesticated Red Jungle Fowl. In the wild, Red Jungle Fowl live in flocks with one rooster for every few hens (where "few" is probably less than five in the wild, though in zoos flocks may be larger and have a higher rooster:hen ratio). Since one rooster can fertilize many hens, in the wild virtually all eggs will be fertilized. Since jungle fowl, of course, lay far fewer eggs than domestic chickens, the cost of the extremely rare unfertilized egg will be low.

In principle, there could be a molecular mechanism that checked for evidence of fertilization before allowing an egg to be laid, but of course such a mechanism would have its own costs, and would almost never actually be useful.

Why do Chickens lay unfertilized eggs?

It turns out that I completely misunderstood how chickens and eggs work. I was assuming that in a regular chicken farm, we do something to the hens to make them lay unfertilized eggs, as opposed to what I would assume to be the natural order of things, laying fertilized eggs. Instead chickens naturally just lay a bunch of "useless" (to them) eggs.

To what end? It seems like an immense waste of energy and resources to simply supply predators with an easy food source.

And since chickens do this, do other birds lay large amounts of unfertilized eggs as well? Turkeys? Sparrows? Dinosaurs?

** edit ** I realize what unfertilized chicken eggs are. What I'm asking is why. And why so often.

What is happening to this subreddit? So many bullshit answers on here! Once and for all - one, a chicken laying an egg is NOT remotely the same thing as the human period, and two, this is AskScience, which means, "keep your posts free of layman speculation ". Thank you.

Also this question came up a couple weeks ago. (here)

Anyway - most birds, once they get the "right" cues to start laying eggs (right daylength, right environment, & usually the presence of a male), will enter a cycle of egg production in which they lay one egg every morning until the clutch is complete (this might be just 2 days - i.e. 2 eggs - for sandpipers, 5-7 days for most songbirds, a dozen days or more for most of the pheasant/chicken family). Once that egg-laying process is started they have a very difficult time stopping it and even if the male suddenly disappears in mid-laying of the clutch, usually the female has to go ahead and lay the rest of the clutch (i.e. she has to lay unfertilized eggs). For most wild birds though there is almost always a male nearby willing to "step in", so to speak, and also, the whole egg-laying process only takes a week or two. We have bred domestic chickens to (a) initiate egg-laying even when no male is around, (b) extend the egg-laying period for some 200+ days instead of the original 12-24 days of their wild ancestors (red junglefowl).

Also. About whether or not this is analogous to a human period. NO. It's really not. I know what you guys are getting at: women release unfertilized eggs too. But they don't do that during the period. They do it 2 weeks earlier. The human egg does not come out during the period. So this is entirely the wrong analogy. Birds are getting "stuck" in what is comparable to the middle of the human cycle, the day of ovulation, repeating that day over and over. The period is, hormonally and physiologically, much more comparable to what happens to a bird at the end of the season when she shuts down ovulation entirely and shuts down the oviduct for the rest of the year.

And then, even if you compare ovulation in mammals to ovulation in birds, there are some huge differences. The cost is much greater for birds. Mammals release a tiny ovum with hardly any yolk. Birds grow the ovum up to enormous size (an inch in diameter for chickens) over a period of several weeks, depositing a huge amount of yolk in it. During this period the liver is making yolk like crazy and sending it through the blood to the oviduct to be put in the egg the bird's blood is full of yolk fats and yolk proteins. Once the ovum has gotten this large it is difficult to halt the process and difficult to reabsorb the ovum at this point it's physically hanging out the side of the ovary, barely contained by the thinnest of membranes. At this point the bird really just has to pop the thing out. So, it gets ovulated, then the oviduct puts all the egg white on (this is a substantial production of protein and water) then the egg's respiratory membranes go on (these are those thin layers that you see when you peel a hard-boiled egg) then the bird goes through a several-hours-long wave of substantial osteoporosis, breaking down her own bones to produce enough calcium to make the shell. Finally the pigment layer goes on. It's an incredible process and it's a huge cost. They do all this in exactly 24 hours, too. (almost to the minute.) It's a much more serious investment than a mammal's egg. ANYway, once the process is underway the female bird cannot seem to stop it she has to go ahead and lay. She makes the initial decision about 2 days before laying of the first egg, based on a variety of cues. If the male disappears right then, she's basically screwed (or, well, not.).

What does a hen do with her unfertilised eggs?

A hen does not know if her eggs are fertilised or not. In fact (much like a human) a rooster can be infertile, so a hen's eggs might not be fertilised even if she is in a flock with a rooster.

Many modern breeds and commercial hybrid hens will do nothing with their eggs other than lay them and walk away. Many have had the instinct to brood [sit on their eggs to hatch them] bred out of them over generations. In a modern egg production facility, you do not want a hen to "go broody". When hens are ready to raise chicks, they will stop laying eggs for that period and it's very hard to convince them to give up the idea.

This does not mean that no hens will brood eggs many breeds still retain their instincts to mother. Silkies, for instance, are renowned for their desire to sit on eggs. Other breeds, such as Orpingtons, Brahmas, Cochins, Marans, Cornish, and others go broody quite regularly. When a hen that has broody instincts lays an egg, she is forming a 'clutch' of eggs. She does nothing to care for these eggs other than hide them in a secure place until she is ready to sit on them. She will continue to lay eggs in this clutch until she has 'enough', which is a number anywhere from seven to as high as 20-plus. Once there are 'enough' eggs, a hormonal switch will occur that will put her into what's best described as a broody trance. She will stop laying eggs and begin to sit on them instead.

There are very good reasons that she does not sit on the eggs from the beginning. Firstly, she needs to continue to eat and drink so that she doesn't lose body condition and can continue to produce eggs for her clutch. Secondly, all the eggs need to begin developing on the same day. An egg does not start forming a chick as soon as it's laid. Instead, the eggs are kind of in a state of suspended animation. Once an egg is above about 98 degrees Fahrenheit for approximately 24 hours, however, it will begin to develop. This way, all the chicks start developing when the hen settles down to sit on them and are all developing at the same time. Then all the chicks will hatch over a short period (usually less than 24 hours) and are all ready to venture out for food.

Two to three days after the first chick has hatched, the mother hen will come out of her broody trance and start to care for the chicks. In the meantime, the chicks will all stay under the mother and require no food or water they are fed from the remnants of the yolk that is in their body for this purpose. The mother will care for them for a while – the exact time is different for each mother hen. Some care for them only until they are 12 weeks old, some will care for them longer.

This is an edited answer from What does a hen do with her unfertilised eggs? which originally appeared on Quora: The best answer to any question. Ask a question, get a great answer. Learn from experts and get insider knowledge. You can follow Quora on Twitter, Facebook, and Google+.

What Is the Difference Between Fertilized Eggs and Unfertilized Eggs?

The horror of cracking open an egg in your kitchen to find a dead, bloody baby chick inside is more of a fear than fact. True, it happened to me once and I didn’t eat eggs for a few years afterward. But that is very, very, very rare, eggsperts say. Sorry (not sorry!) for that pun. Edible egg advocates even say it never happens.

Regardless, the average consumer buying a carton of chicken eggs at the store or farmers market can’t tell the difference between a fertilized egg and an unfertilized egg from outside the shell. Chances are you’ve never eaten a fertilized egg, because nearly all eggs sold commercially are produced by hens that have not mated, says Lauren Cobey, media representative for the American Egg Board.

Size Matters Large & Extra Large Eggs: Is There That Much Difference? The difference between fertilized and unfertilized eggs comes down to whether a rooster has been involved or not. Hens do not need a rooster to lay an egg they do so (almost daily) on their own simply according to light patterns. However, if a rooster does mate with a hen, the eggs she produces are fertilized and, under the right incubation conditions, can bear chicks. No rooster means zero possibility of the egg ever becoming anything more than that.

When fertilized eggs are sold for consumption, there is no danger of eating a developing embryo, says Cobey, for a few reasons: All eggs sold in the United States as food must be refrigerated, a process that halts any growth inside the shell. Also, the interior of any egg intended to be sold as food must be inspected—accomplished by shining a bright light through the shell (called candling)—which highlights any irregularities, such as a developing chick. These regulations hold true whether the eggs are intended for a large chain like Safeway or for the farmers’ market. Eggs with irregularities never make it to retail and are destroyed (except for that one time).

Nutritionally, says Cobey, fertilized and unfertilized eggs are the same. They also taste the same, says Kathy Shea Mormino in her “Facts & Myths About Fertile Eggs” article on her blog, The Chicken Chick. Mormino is an attorney as well as a backyard-chicken keeper, advocate, and educator who’s appeared in The Wall Street Journal, Associated Press and on local and national TV, radio, and podcasts.

If you find a blood spot inside an egg, it doesn’t mean that egg was fertile either, Mormino says. A blood vessel and rupture at any point in a hen’s reproductive system as a result of a vitamin A deficiency, genetics, or some random occurrence. People may think so because fertile eggs develop veins around day 4 of incubation, but it doesn’t look like a blood spot.

That said, if you’re still on board with eating eggs, as I am several years after that traumatic childhood experience, we have some delicious (unfertilized) egg recipes you gotta try.

What Is Brooding and Why Is My Hen Doing It?

What is brooding?

Brooding is a natural instinct that many chickens have to set on their next and hatch a clutch of eggs. It is an overwhelming desire to sit on the clutch, incubate the eggs, hatch them and mother a brood of chicks. Some breeds are more prone to it than others and for those looking to keep egg production up it can be a bit frustrating.

Why is my hen brooding and how can I tell when she’ll start again?

It’s difficult to tell when a hen may become broody, though generally if a hen is going to start they will be more prone to it in the spring months and with hens that are about two years old. Hens are also more prone to brooding if eggs aren’t collected regularly (read everyday). There are some breeds of chickens that have had broodiness bred out of them.

Because brooding is the desire to hatch a clutch of eggs, the broody hen can become quite temperamental and even peck a hand trying to retrieve eggs that are being set on. They will sit on the nest for weeks, though 21 days is all that is necessary and egg production will cease. Unfertilized eggs will never hatch and if they are not retrieved will simply spoil and you’ll have lost a whole clutch of eggs.

Note: If a hen has not been mated to a rooster ALL eggs are unfertilized. Eggs will only hatch if they have been fertilized which requires a rooster. A hen will lay eggs every day regardless of the presence of a rooster.

Brooding for the long term can be detrimental for your hen. They will neglect their own needs, such as food and water. They become vulnerable to parasites as they are not remaining clean. It can also be upsetting for your other birds as one nesting box is constantly occupied by a cranky, pecking hen.

Discouraging broodiness should be done as soon as noticed if you do not want to hatch chicks or know your eggs won’t hatch. Keep an eye out for any hen that wants to spend more and more time in the nesting box or hens that are getting a little cranky and pecky. Block off the nesting box and remove the eggs. If this doesn’t work, you may need to move her to a temporary box and keep her away from her normal laying places. For exceptionally stubborn hens, set them in a location that is cool. By keeping their lower areas cool you will discourage the behavior.

If your hen is brooding and you want some chicks, let her do her job. Be careful, however, that the brooding mother isn’t bullied. If other chickens are forcing her away from her nest move them all, eggs and hen, to a new location late at night while the hen is sleeping. Make sure that your brooding hen leaves at least once a day to eat, drink and poo be warned, brooder poo is particularly disgusting. You must be vigilant! Some broody hens will not take care of themselves. If you have not seen her move in 24 hours, pick her up and carry her to food and water. She may begin to look thin and anemic, but if you are keeping her parasite free and eating and drinking, then 21 days later when the chicks hatch she’ll regain a more normal routine and get back to her old self.

Pigeons keeps on laying unfertilized eggs

my pigeons got egg but this time they only have 1 and i was able to candle it and its fertiled but according to my reading pigeons normally lay a pair of eggs. why do my pigeons only have 1 and its almost a week and nothing follows. please help. In a "PERFECT WORLD" yes pigeons lay 2 eggs you are correct ,

I would doubt any one could tell you with any certainty why this time you only got one egg. Age is a big factor. Not quite mature or getting to old as well. Diet is another part of the equation. Hope you have better luck next time it happens.

Sometimes only one squab survives. Sometimes they will abandon the squabs completely. It is part of the hobby of pigeon fancying. If this egg hatches and squabs survives I would pat yourself on the back and say you are doing a good job and all you can do. I know you are doing more thing right than you are wrong for sure. Good Luck Jhandha.

Why do chickens lay unfertilized eggs?

When a rooster actively mates the hens the eggs produced can be fertile for as long as 2 - 3 weeks at a stretch.

No rooster no fertile eggs.




Positively Ducky

Breeding for egg laying traits resulted (over time) in chickens (as well as some breeds of ducks) laying all the time.

But will an unmated wild duck still lay a clutch and try to hatch out unfertile eggs?




Rest in Peace 1949-2012

Lots of bird will lay without mating. Even parrot and etc.

The longer spring daylight triggers the egg laying in the hens,even if no male around. Quail, pheasants, and etc.

Now some birds may have to mate to lay. But not all, my guess those that dont pair up would lay with or without a male.




Rest in Peace 1949-2012



Yes, chickens, ducks, turkeys, geese, etc - poultry females will lay eggs and go broody even without a mate. They will do their best to sit and hatch unfertile eggs. The absence of a mating male really has nothing at all to do with the hormonal influence and natural instict.

There is a phenomenon that is rare but does happen and has been proven in laboratory testing. Some unfertile eggs can begin to develop.

Do hens lay unfertilized eggs?

Most chicken eggs produced for consumption are unfertilized. Eggs found in the grocery stores are typically produced by chickens that never come in contact with a rooster.

In backyard flocks, however, there is usually a rooster present with the hens and he ensures that the eggs are fertilized by mating the hens regularly. Eggs from hens who have been mated in the past week are fertilized chicken eggs. They can be eaten or incubated and hatched into chicks.
Yes, hens can and do lay unfertilized eggs. In fact, most grocery store eggs come from hens that have not been mated by a rooster and therefore are unfertilized.
Yes, a hen that has not mated with a rooster in the past ten days will lay only unfertilized eggs. A hen that has never been with a rooster will only lay unfertilized eggs.

A rooster must mate a hen for her to lay eggs, and after she is first mated it will still take about a week for her eggs to be fertilized, as it takes about that long for the rooster's sperm to travel to the hen's ovaries where her eggs are fertilized before the shell covers them and before they are laid.

Fertilized Vs. Unfertilized Chicken Eggs: What You Need to Know

There is always debate going on fertilized vs. unfertilized chicken eggs. So, what are both and what are the factors that distinguish both from each other? Keep reading to learn about the various differences between fertilized and unfertilized chicken eggs.

There is always debate going on fertilized vs. unfertilized chicken eggs. So, what are both and what are the factors that distinguish both from each other? Keep reading to learn about the various differences between fertilized and unfertilized chicken eggs.

The debate about ‘what came first – chicken or egg’ is an old one. This debate is endless, which seems to have almost no conclusion or many confusing conclusions. However, the debate of fertilized vs. unfertilized chicken eggs is a simple one, which is based on facts that you yourself can check. There are many differences between fertilized and unfertilized chicken eggs right from their formation to their nutritional content. Let us look at these factors which distinguish fertilized and unfertilized chicken eggs in detail.

Formation of the Egg

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This is the most basic difference between fertilized and unfertilized chicken eggs. Understanding this main difference will help you clear your doubts on these two types of eggs. Here is one important fact – ‘a hen can keep laying eggs despite mating with the rooster’. So, a hen can go on laying eggs even if the rooster is not involved. These eggs are unfertilized eggs. This means these eggs will never hatch. But, when a rooster mates with a hen, then hen can go on laying fertilized eggs. A fertilized egg has a potential of hatching some day into a chick. However, a certain environment and care needs to be taken of this egg for it to hatch into a chick. The fertilized egg need to be kept at a certain warm temperature for it to hatch.

Distinguishing Both by Candling

Candling is the process which can help you distinguish between both the eggs without having to break them. For this process, a candler is used on the egg. The process is carried out in a dark room. Candler can be a small flashlight or any other source of light shone on the egg. Hold the egg at slanting angle so that you can observe its width. Turn it to the left and right, and view the contents present inside the egg. If an egg appears opaque to you, then it is a fertilized chicken egg. Sometimes development in the egg might not be seen even if it is a fertilized one, for this purpose, keep it for few days for incubation and then observe.

Distinguishing Both by Breaking Them

Another way to check if the egg is fertilized or not, is to break them open. Simply, break the egg and observe it in the center of the yolk. If you observe a white spot or a white ring in the egg yolk, (yellow part) then the egg is fertilized. If you don’t see any white formation in the center of the egg yolk, then it is not a fertilized egg. Apart from this sign, a fertilized egg can also show tiny red lines running along the surface of the egg yolk. These signs show that the embryo is present in the egg.

Debate on Health Benefits

Many people say that a fertilized chicken egg is more healthy. However, this is not true as both types of eggs are healthy and have almost same nutritional value. Eggs are one of the healthiest food, and good for people of all ages. But, if you store any egg for long, then it will start to lose its protein content. Also, if fertilized eggs are stored in the fridge, then they will not hatch.

Debate on Vegetarian Egg

There is argument going on unfertilized egg being vegetarian. This is not entirely true. For an egg to be called a vegetarian egg, the hen should be given a completely vegetarian feed. Also, the egg should not be fertilized. This type of egg is called vegetarian. This type of egg doesn’t have life in it so considered by many as vegetarian. Still many vegetarians refrain from eating such eggs.

I hope this article cleared your doubts on fertilized and unfertilized chicken eggs. So, next time you break an egg open you will know if the egg was a fertilized one or an unfertilized one.

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