Applied Research Note: Internal organ colonization and horizontal transmission of experimental Salmonella Enteritidis and Salmonella Kentucky infection in vaccinated laying hens in indoor cage-free housing
Cage-free housing of laying hens may provide opportunities for widespread environmental distribution of Salmonella contamination and horizontal transmission of infection within flocks. Salmonella Enteritidis in commercial laying flocks presents an ongoing public health concern because reproductive organ colonization in hens leads to deposition inside eggs. Many S. Enteritidis control programs include vaccination to induce protective immunity against infection. Salmonella Kentucky is common in egg production environments but has not been associated with egg contamination. This study compared the invasion of internal organs and horizontal spread of infection during the first 2 wk after experimental S. Enteritidis and S. Kentucky infection of previously vaccinated laying hens in indoor cage-free housing. Two groups of 72 hens each were housed in isolation rooms simulating commercial cage-free barns and 1/3 of the hens were orally inoculated with either S. Enteritidis (1 room) or S. Kentucky (1 room). At 6 and 12 d after inoculation, half of the hens in each room were euthanized and samples of the liver, spleen, ovary, oviduct, and intestinal tract were removed for bacteriologic culturing. Among hens inoculated with S. Enteritidis, 66.7% of the intestinal, liver, and spleen samples were positive for the pathogen at 6 d after infection, as well as 41.7% of intestines and 16.7% of livers from contact-exposed hens. Significantly (P < 0.05) fewer hens were colonized by S. Kentucky. These results demonstrate that vaccines may not always provide complete exclusion of Salmonella. In cage-free housing systems, vaccination should be supplemented with a comprehensive risk reduction effort to prevent extensive horizontal dissemination of Salmonella.
