Abstract
Commercial poultry hatcheries potentially provide a sanitary barrier between breeder flocks and their progeny. This is important, particularly within the pyramid breeding structures in integrated poultry production systems. However, the operation of hatcheries and their focal position connected with multiple flocks, both on the input and output sides, means that they are vulnerable to being reservoirs of infectious agents. Of particular concern for hatcheries is the pseudo-vertical transmission of bacteria that are initially deposited at the surface of forming or freshly laid eggs. These bacteria (of which Salmonella enterica is a prime example) can subsequently be present in the chick, as well as spreading within the hatchery environment to colonise other hatching birds. Furthermore, if such infectious organisms become persistent in parts of the hatchery environment, this allows their repeated transfer to hatching individuals or even (via personnel and fomites) to transfer back into breeding flocks supplying the hatchery. The use of antimicrobial drugs in hatcheries adds the further hazard of seeding progeny with antimicrobial-resistant (AMR) organisms. The mechanisms of hatchery, egg and subsequent chick contamination have been understood, and strategies to counteract the spread and persistence of infectious agents are well-established. However, many studies examining bacterial pathogens and AMR organisms in poultry production implicate hatcheries, either as a link in a chain or as a source of such agents. This review outlines the challenges posed by hatchery operation to control of bacterial transmission, it examines the contemporary and historical evidence for such phenomena, and it briefly discusses strategies to counteract the issue.