An egg weights about 60g in average, and a hen 3kg, how the hen can produce every day something about 2% of it’s weight like this? Which kind of metabolism the hen have to achieve this?
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They spend plenty of time eating. Pretty much their whole existence is eating in order to lay eggs
Oh that’s not even all. If you manipulate the day/night cycles with artificial lights, you can get them to lay 8 eggs per 7 days.
Domestication changes things in terms of frequency and size, but most birds (and reptiles) will either reabsorb the egg if it’s not fertilised or eat it. It’s a waste of energy and time but the nutrients aren’t wasted.
Years of selective breeding.
The Red Jungle Fowl (almost certainly the ancestor of all modern chooks) have some sub-species that breed throughout the year, so lay eggs through out the year (yay! tropics).
These birdy-birds were domesticated at least ~~80,000~~ 8,000 years ago, and over that period of time they were selectively bred to lay almost daily.
The short answer is that it is dangerous for them. Their lifespans are shortened and they die of some bone deficiency. Add that to selective breeding to serve our interests and not their health, and you have chickens that lay eggs like well tuned machines until their body has to choose between feeding their bones calcium or building egg shells… and it chooses the shells.
We‘ve bred them to this point.
Chicken are Gallus Gallus Domesticus. Their wild counterparts are other Gallus Gallus subspecies, commonly called junglefowl. These lay an estimated 10-20 eggs a year in the wild.
Over the millennia we‘ve always chosen those chicken that lay the most eggs, so now we have hens laying an egg almost every day. Layer hens are fed a lot. Their existence is basically eating, laying eggs, eating, laying eggs.
They eat around 100 to 150 grams of feed each day. That‘s 5% of their bodyweight. For comparison an average human eats roughly 1.2kg per day, with an average weight of 80kg thats less than 2%
Chickens come from birds who had a special ability to multiply very very quickly when given enough food to do so. This was because their food supply was inconsitent(bamboo sprouts every like 10 years or some shit). This mechanism is what have used to make chicken grow and lay eggs super fast. Obviously chickens do need energy to do this, so chickens eat way more than most animals per bodymass.
It’s not like each day, they create a whole egg. I used to raise layer hens. Occasionally one would need to be killed, for instance, if it had been badly injured by a predator.
If you see the inside, chickens have an egg “chain”, a number of eggs at increasing stages of development in them.
And, as others have noted, they spend the day eating, scratching the ground, eating and roosting when the sun goes down. Mine had a diet of rich gain feed, plus foraging in the garden.
We’ve selectively bred them to produce eggs daily for about a year, when they are killed for cheap meat or pet food. If they aren’t killed because they’re no longer economically beneficial (their egg laying rate drops off) they often die prematurely due to bone density problems because calcium is diverted from the bones to the eggs, or cancers of the reproductive system due to their supercharged hormonal cycles. Many rescue centres actually administer hormonal contraceptives to their chickens to protect against this. Naturally domestic chickens can live for about 5 to 10 years, but commercial egg layers are typically killed at 1 year when their bodies are worn out.
They do have to eat a lot to sustain this, part of the reasons eggs are so expensive is that their feed prices have increased a lot lately too, and as they eat so much it has a big knock on effect on the egg prices.
tl;dr, yes it’s very physically exhausting to them, it literally kills them.
Some breeds lay more eggs than other. I read once that a chicken is either built for eggs or meat. My best laying chickens (6eggs weekly) are fairly small and lean. All their energy goes to egg production. Like others have said, chickens spend all their time eating lol.
My not-so-great layers (2-3 eggs weekly) are round little chubsters. Their energy is divided between staying plump and egg production.
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