FIG. 4.

(Top panel) Integrated structure of the commercial poultry production system. Production companies acquire breeder flocks from the pedigree flocks owned by three to five companies worldwide. These breeder flocks produce hatching eggs that become meat birds and layers for human consumption. (Lower panel) Potential sources of antibiotic-resistant bacteria for poultry. While antibiotic use may select for resistant populations (left box), young chicks lacking a stable intestinal bacterial community may be more susceptible to colonization with resistant strains present in the hatchery or on the farm (middle box). Exposure of hatchlings to resistant bacteria present on the surface of the egg can potentially result in dissemination of resistant strains from the breeder flock to progeny (right box).