<P> On average, a chicken lays one egg a day for a number of days (a "clutch"), then does not lay for one or more days, then lays another clutch . Originally, the hen presumably laid one clutch, became broody, and incubated the eggs . Selective breeding over the centuries has produced hens that lay more eggs than they can hatch . Some of this progress was ancient, but most occurred after 1900 . In 1900, average egg production was 83 eggs per hen per year . In 2000, it was well over 300 . </P> <P> In the United States, laying hens are butchered after their second egg laying season . In Europe, they are generally butchered after a single season . The laying period begins when the hen is about 18--20 weeks old (depending on breed and season). Males of the egg - type breeds have little commercial value at any age, and all those not used for breeding (roughly fifty percent of all egg - type chickens) are killed soon after hatching . Such "day - old chicks" are sometimes sold as food for captive and falconers birds of prey . The old hens also have little commercial value . Thus, the main sources of poultry meat a hundred years ago (spring chickens and stewing hens) have both been entirely supplanted by meat - type broiler chickens . </P> <P> Traditionally, chicken production was distributed across the entire agricultural sector . In the 20th century, it gradually moved closer to major cities to take advantage of lower shipping costs . This had the undesirable side effect of turning the chicken manure from a valuable fertilizer that could be used profitably on local farms to an unwanted byproduct . This trend may be reversing itself due to higher disposal costs on the one hand and higher fertilizer prices on the other, making farm regions attractive once more . </P> <P> From the farmer's point of view, eggs used to be practically the same as currency, with general stores buying eggs for a stated price per dozen . Egg production peaks in the early spring, when farm expenses are high and income is low . On many farms, the flock was the most important source of income, though this was often not appreciated by the farmers, since the money arrived in many small payments . Eggs were a farm operation where even small children could make a valuable contribution . </P>

Where does most of the chicken in the us come from