Horizontal transmission of Salmonella Enteritidis in groups of experimentally infected laying hens housed in different housing systems

Concerns regarding the welfare of laying hens have led to the ban of conventional battery cages in Europe from 2012 onward and to the development of alternative housing systems that allow hens to perform a broader range of natural behaviors. Limited information is available about the consequences of alternative housing systems on transmission of zoonotic pathogens such as Salmonella Enteritidis. However, Salmonella enterica serovar Enteritidis continues to be one of the leading causes of bacterial foodborne disease worldwide and this is mainly attributed to the consumption of contaminated eggs. A transmission experiment was performed to quantify the effect of the housing system on the spread of a Salmonella Enteritidis infection within a group of layers and on internal egg contamination. At the age of 16 wk, 126 birds housed on the floor were inoculated with Salmonella Enteritidis. Three weeks later, the inoculated hens were housed together with equal numbers of susceptible contact animals in 4 different housing systems: a conventional cage system, a furnished cage, an aviary, and a floor system. Transmission and egg contamination were followed during a 4-wk period. A trend toward increased bird-to-bird transmission was detected in the aviary and floor system compared with the cage systems. Also, significantly more contaminated eggs were found in the aviary compared with the cage systems and the floor system. These results suggest that there is a clear need to optimize and maintain Salmonella surveillance programs when laying hens will be moved from conventional cage systems to alternative housing systems.