Modern high-volume poultry farms, with rows of cages stacked indoors for control of heat, light, and humidity, began to proliferate in Great Britain about 1920 and in the United States after World War II.
Females are raised for meat and for their edible eggs.
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Only hens that could no longer produce enough eggs were killed and sold for meat.
By the mid-20th century, however, meat production had outstripped egg production as a specialized industry.
Females are raised for meat and for their edible eggs.