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?
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.
They spend plenty of time eating. Pretty much their whole existence is eating in order to lay eggs