Prior to WWII, the majority of poultry were reared in backyard flocks on dirt-floored pens, in small sheds with natural or make-shift ventilation.
Between 1940 and 1960, advancements in nutrition and genetics allowed the broiler market to shift from being able to produce a 3-3.5 pound bird at 16 weeks to one that only took 8 weeks. Due to advances in production efficiency and refrigerated trucking, markets expanded to a much larger geography while the price of poultry per pound dropped dramatically from approximately 65 cents in 1940 to 29 cents in 1960. Due largely to changes in price versus other meat options, demand for broilers increased dramatically. Production systems during this time also underwent dramatic changes from the seasonal, small backyard sheds to large year-round naturally ventilated buildings and during some seasons, large outdoor pens.
Turkey and broiler flocks are reared in enclosed buildings with updated equipment. For instance, birds are now reared in confinement with on-demand feeder lines, on-demand cup or nipple waterers, or on-demand bell-type waterers. These developments overcame most problems with weather, predators, potential pollution from lot runoff, and allowed the use of more intensive production schedules. Almost all turkeys and broilers are reared on litter floors. Ducks, turkeys, and occasionally broilers are reared in multi-stage facilities with facilities for brooding birds, and in larger facilities (either a separate room or separate building) that they will be moved into at an older age.
Young pullets, laying hens, and broiler breeders are reared in either wire-cages or slotted-floor systems. If a slotted flooring system is used, there may or may not be a central area containing litter. Duck facilities encompass a number of different production types and may or may not have multistage facilities. Systems in use include all-litter houses, raised-wire flooring over a shallow pit (which would be located below a nipple water line) and houses with raised-wire floors.
Layers in commercial facilities produce a great deal of body heat. Ventilation to keep the hens cool is usually more of a concern than providing heat in winter. Non-brooding birds (3-4 weeks and older) grow best at around 70-75 degrees. In winter, they are protected from winter winds in an insulated building. Enough ventilation must be provided to remove moisture produced by the animals and to provide fresh air. In summer, large sidewall vents are opened or large ventilation fans are operated to keep the animals comfortable. This is referred to as either naturally ventilated (air change due to the wind) or mechanically ventilated (where air is drawn into the buildings through vents due to a negative pressure created with wall fans that exhaust inside air to the outdoors. Further information on poultry ventilation.
Disadvantages associated with large enclosed, production facilities are that different ages of birds with different degrees of disease resistance are housed in close proximity which can facilitate disease spread if adequate cleaning and disinfecting are not feasible in some situations, and higher levels of medication may be required to control disease. The primary rule of thumb for workers on a farm with multiple ages of birds is to always travel from the youngest birds on the farm to the oldest, and not vice-versa. Biosecurity plans between farms, and between multiple production buildings on the same farm can help reduce the incidence and spread of disease from one flock to the next.