So, in order for a birth to occur, there must be a male contributing sperm and a female contributing the egg. Same thing as with pretty much all creatures. Chickens, like most birds, have the whole pregnancy thing happen outside of them rather than keeping the egg inside of their body the whole time. Eggs that hatch have a sperm that fertilized them, while eggs that we eat are unfertilized. Even if there is no male, the chicken still lays eggs.
As with all farmed animals, we have spent thousands of years creating animals with the traits we want. In the case of chickens, this means âconstantly laying eggsâ.
The eggs we eat come from chickens who *didnât* mate with a rooster. The eggs that hatch comes from the ones who *did*. Itâs still the same egg either way; it just depends on whether or not it was fertilized.
Iâve been raising chickens for almost 20 years. Hens lay an egg almost every day, whether theyâre having sex or not.
If a hen and rooster hen have sex, that henâs eggs will be fertile (meaning, they *could* hatch into baby chicks) for at least a few days. Theyâre still perfectly fine to eat, but if they were incubated for 21 days, they would hatch into baby chicks.
Eggs you buy at the store come from giant farms full of nothing but hens, there are no roosters around, so no sex is happening, meaning those eggs are not fertile and could never hatch. Roosters have no effect on egg production, thus they are not needed.
The only difference between the eggs we eat and the eggs that turn into chickens that hatch is that the eggs we eat arenât fertilized, meaning the male rooster doesnât insert any sperm into the female hen. Hens will lay eggs whether or not theyâre fertilized.
Hens donât get pregnant in the sense that youâre thinking of because thatâs a term that applies to animals that have live young. Roosters insert their sperm into the hen with their cloaca (a cloaca is like is a single opening that is used for both reproduction and excreting waste) and the sperm fertilize the egg inside the hen, but then the hen passes the egg out of her own cloaca. The embryo inside then grows, develops, and hatches all outside of the hen.
Just to address the â how do they lay eggs all the time?â part. Chickens evolved from a wild bird species that lives in Southeast Asia, in places with a lot of bamboo forests. Bamboo forests will produce a whole bunch of seeds all at once, but only every few years. The wild proto chicken evolved reproductive cycles to take advantage of this. Basically they have a little genetic switch inside them, and if they have access to a bunch of food for long enough the switch flips, And they go into crazy egg laying mode. Their body just constantly starts producing as many eggs as it can as often as it can. The idea was that when food was scarce they wouldnât have many babies and population might dwindle, but every few years when they had TONS of food they took advantage of it and made tons of babies. Humans observed this behavior and figured out how to take advantage of it. If we give chickens a nice place to live and enough food, we can trick them into flipping that switch and making a bunch of eggs (in chicken farming they call this going âon broodâ or âgoing broodyâ).And if we then keep the roosters from being able to access the female chickens, we can make sure all of those eggs are unfertilized for us to eat. So just like we saw wolvesâ ability to hunt in a coordinated fashion and said âohhhh, I can DO something with that!â And turned them into dogs, we saw Red Jungle Fowlâs ability to make a TON of eggs when the conditions are right and turned them into chickens.
Chickens lay eggs all the time. The ones that hatch were fertilized by a rooster, the ones that donât, werenât.
If you look closely at a chicken egg, thereâs a little white squiggly bit on the yolk. Thatâs the actual egg cell, which develops into a chick. The yolk is the food for that chick, and the egg white is there to suspend it all in the egg.
If we compare this to a humanâs reproductive system, a woman enters ovulation, an egg is released. 12-24 hours later, if it isnât fertilized, it will simply die and eventually fall out. About 2 weeks later, if the body doesnât have a fertilized egg implanted into the uterine wall, the uterine wall is shed away with blood as a period. If the egg is fertilized, it can survive 6-10 days before implanting into the uterine wall and eventually developing into a fetus.
Now, back to a chicken. Itâs a similar idea, except domesticated chickens can lay and egg every day if theyâre not brooding.
The egg cell is released, and a yolk is developed, and regardless of whether or not itâs fertilized, a shell is formed around it and it is passed through the cloaca, and an egg is laid.
If the egg is fertilized, it can develop and start eating the yolk until it is mature enough to hatch.
Brooding happens if a chicken is allowed to sit on eggs for too long. The chickenâs hormones switch off egg production so the chicken can save energy and incubate already laid eggs. The chicken cannot tell if those eggs are fertilized or not for a while. Once the chicks are able to move around inside the egg, they can tell, and the chicken will break and eat any eggs with no signs of movement to regain the nutrients.
If youâre farming eggs, and a chicken starts brooding, you should separate them from the other chickens (so she doesnât sit on their eggs) and after a few days the chicken should go back to laying.
If youâre breeding chickens, you can just let nature take its course (if you own a rooster)
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