Poultry housing and the persistence and transmission of Salmonella in egg-laying flocks

The ongoing transition of the egg industry toward increased reliance on cage-free and outdoor housing systems has raised new pathogen control and egg safety challenges for flock managers. This review summarizes current knowledge about how poultry housing systems (conventional and non-cage) influence the persistence, environmental reservoirs, and transmission of Salmonella in commercial egg-laying flocks. Consistently across different types of poultry production environments, salmonellae have been shown to persist in dust, manure, flooring substrates, soil, structural surfaces, and diverse biological vectors, Extended Salmonella survival is especially likely under conditions of high moisture and low airflow. The infection of birds via exposure to environmental reservoirs can be magnified by horizontal dissemination within flocks, which can be especially rapid and extensive when birds are stocked at high densities, can move about and intermingle widely, and share common floor or ground areas. Both cage and non-cage systems have characteristic intrinsic Salmonella risk factors: caging may increase stress-related susceptibility to infection, but cage-free systems may facilitate greater opportunities for exposure to other birds and environmental sources. Accordingly, the design and management of facilities for egg production should incorporate Salmonella risk reduction strategies which target both broadly relevant and housing-specific vulnerabilities to bacterial transmission and persistence.