Environmental contamination and internal organ colonization by Salmonella Enteritidis in experimentally infected cage-free layer pullets reared in-place or relocated after simulated transport.

The production of contaminated eggs by laying hens infected with Salmonella Enteritidis continues to present an international public health challenge. This study assessed how 2 different cage-free layer pullet rearing plans influenced environmental contamination and internal organ colonization after experimental infection with S. Enteritidis at 2 different ages. In 2 trials, birds were orally inoculated either as chicks at 1 wk of age or as pullets at 10 wk of age. In each trial, half of the birds were maintained entirely in-place and half were subjected to a transport and relocation treatment at 14 wk of age, simulating the common commercial practice of moving pullets from rearing to laying houses at that time. Environmental samples collected from each room at intervals after infection and internal tissues harvested at 16-17 wk of age were cultured for S. Enteritidis. The most sensitive detection of S. Enteritidis in the housing environment was obtained using flooring substrate composite samples (46%), and significantly less efficient detection was achieved via dust sampling (14%). The overall frequency of S. Enteritidis recovery from environmental samples was significantly greater in rooms housing birds infected at 10 wk of age than in rooms of birds infected at 1 wk (55 vs. 21%) and a similar pattern was observed for S. Enteritidis recovery from internal organs. The simulated transport stress treatment applied in this study did not affect either subsequent environmental contamination or internal organ colonization with S. Enteritidis. Isolation of S. Enteritidis from environmental samples in rooms housing relocated birds was infrequent (6%). S. Enteritidis was recovered significantly more often from spleens and ceca of birds infected at 10 wk and kept in-place than from similarly infected birds that were relocated (15 vs. 6% and 18 vs. 7%, respectively). These results suggest that continuing exposure to contaminated housing environments by flocks maintained in-place has the potential to perpetuate S. Enteritidis infections during the final stages of rearing before attaining reproductive maturity and commencing egg production.