Internal organ colonization by Salmonella Enteritidis in experimentally infected layer pullets reared at different stocking densities in indoor cage-free housing

Authors: Gast, Richard; Jones, Deana; Guraya, Rupinder - Rupa; Garcia, Javier; KARCHER, DARRIN - Purdue University

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2022
Publication Date: 11/1/2022
Citation: Gast, R.K., Jones, D.R., Guraya, R., Garcia, J.S., Karcher, D.M. 2022. Internal organ colonization by Salmonella Enteritidis in experimentally infected layer pullets reared at different stocking densities in indoor cage-free housing. Poultry Science. https://doi.org/10.1016/j.psj.2022.102104.
DOI: https://doi.org/10.1016/j.psj.2022.102104

Interpretive Summary: Eggs contaminated by Salmonella Enteritidis are often implicated as sources of food-borne human illness because this pathogen can be deposited inside eggs after it invades to the internal organs of infected hens. The commercial egg industry is gradually implementing a transition from traditional cage-based housing to alternative systems to comply with animal welfare goals, but the food safety ramifications of this change remain incompletely understood. The present study assessed internal organ colonization and bird-to-bird (horizontal) transmission by S. Enteritidis in egg-type pullets reared at 2 different stocking densities in indoor cage-free housing. After pullets were reared at either high or low stocking densities (in terms of floor space per bird), they were moved at 16 wk of age to isolation rooms simulating commercial cage-free barns, with nest boxes, perches, and floors covered by wood shavings. One-third of the pullets in 2 rooms were orally infected with S. Enteritidis immediately after placement, and pullets in the other 2 rooms were similarly infected at 19 wk of age (at or near the point of sexual maturity). During the course of the first 2 wk after each introduction of infection, birds were euthanized and their internal organs were tested to detect the presence of S. Enteritidis. The frequency at which the pathogen was found in tissues did not differ significantly between groups of pullets reared at high and low stocking density following infection at either age. However, S. Enteritidis was isolated significantly more often in internal organ samples collected from groups of birds infected at 19 wk of age than from those infected at 16 wk. These results suggest that the susceptibility of young hens to invasive S. Enteritidis infection may increase around the time of reproductive maturity, emphasizing the importance of risk reduction at this critical stage in the egg production cycle.

Technical Abstract: Contamination of eggs by Salmonella has often been identified as a source of food-borne human illness. S. Enteritidis is deposited inside eggs when invasive infections of laying hens reach reproductive organs. The susceptibility of hens in cage-based housing systems to S. Enteritidis has been associated with their stocking density, but the applicability of this information to extensive (cage-free) systems is uncertain. The present study assessed internal organ colonization by S. Enteritidis in egg-type pullets reared at 2 different stocking densities in cage-free housing. Pullets were reared at either 374 square cm or 929 square cm of floor space per bird. At 16 wk of age, groups of 72 pullets were moved into isolation rooms simulating commercial cage-free barns; 1/3 of the pullets in 2 rooms were orally inoculated with S. Enteritidis immediately after transfer and pullets in 2 rooms were similarly infected at 19 wk. At 6-12 d post-inoculation, all pullets were euthanized and samples of liver, spleen, and intestinal tract were removed for bacteriologic culturing. No significant differences (P > 0.05) in S. Enteritidis isolation frequencies from any tissue were observed between high and low density rearing groups following infection at either age. However, S. Enteritidis was found significantly (P < 0.05) more frequently among pullets infected orally at 19 wk than at 16 wk in spleens (68.8% v. 49.0%) and intestines (96.9% v. 84.4%). Likewise, the frequency of S. Enteritidis isolation from all birds (inoculated plus contact-exposed) at 19 wk was significantly higher than at 16 wk in livers (38.9% v. 29.2) and spleens (39.9% v. 28.1%). This increased susceptibility to invasive S. Enteritidis infection at reproductive maturity emphasizes the importance of risk reduction at a critical stage in the egg production cycle.