Internal organ colonization by Salmonella Enteritidis in layer pullets infected at two different ages during rearing in cage-free housing

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

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2024
Publication Date: 6/1/2024
Citation: Gast, R.K., Jones, D.R., Guraya, R., Garcia, J.S., Karcher, D.M. 2024. Internal organ colonization by Salmonella Enteritidis in layer pullets infected at two different ages during rearing in cage-free housing. Avian Diseases. 68:141-144.

Interpretive Summary: The bacterial pathogen Salmonella Enteritidis has often been implicated as causing food-borne human illness because of its ability to contaminate the edible interior contents of eggs after invading to the internal organs of infected hens. The commercial egg industry is undergoing a transition from traditional cage-based housing to alternative non-cage systems, mainly to achieve animal welfare goals, but the animal health and food safety consequences of this change are not thoroughly understood. The present study assessed internal organ colonization by S. Enteritidis in egg-type pullets infected at two different ages after rearing in cage-free floor pens. Groups of pullets were moved into isolation rooms simulating commercial cage-free barns, with nest boxes, perches, and floors covered by wood shavings at either 9 weeks or 15 weeks of age. One-third of the pullets in each room were orally infected with S. Enteritidis immediately after placement. During the first 2 weeks after infection, half of the birds from each age group were euthanized and their internal organs were tested to detect the presence of S. Enteritidis. The remaining birds were similarly tested at 21-22 weeks of age. S. Enteritidis was found significantly more often in the internal tissues of pullets infected at 15 weeks of age than in those infected at 9 weeks of age, when birds were sampled either during the two weeks immediately following infection or at 21-22 weeks of age. These results reinforce the importance of attentive pathogen risk reduction practices during the later stages of pullet rearing for diminishing the likelihood that S. Enteritidis infection will persist until the age at which egg laying commences.

Technical Abstract: The poultry housing environment plays a significant role in the transmission and persistence of the egg-associated pathogen Salmonella Enteritidis in laying flocks. The commercial egg industry is in the midst of a transition toward cage-free housing, but the food safety ramifications of this shift are not yet certain. The present study assessed internal organ colonization by S. Enteritidis in layer pullets reared in cage-free housing and infected at two different ages. Groups of 280 pullets were transferred from the rearing facility (at 9 wk of age in one trial and 15 wk in another) to a containment facility with 4 isolation rooms simulating commercial cage-free barns with perches and nest boxes (70 birds/room). 24 pullets in each room were orally inoculated with S. Enteritidis immediately after placement in the containment facility. At 1-2 wk post-inoculation in each trial, samples of liver, spleen, and intestinal tract were collected from all birds in 2 rooms for bacteriologic culturing to detect S. Enteritidis. At 21-22 wk of age, samples of spleen, ovary, and intestinal tract were similarly collected and tested from all birds in the remaining 2 rooms. Among samples collected at 1-2 wk post-inoculation, S. Enteritidis was isolated significantly more often from groups of pullets infected initially at 15 wk of age than from those infected at 9 wk (61% vs. 38% of livers, 59% vs. 31% of spleens, and 84% vs. 57% of intestines). Among samples collected at 21-22 wk of age, the frequency of recovery of S. Enteritidis was again significantly greater in birds infected at 15 wk of age than in those infected at 9 wk (16% vs. 6% of spleens, 9% vs. 1% of ovaries, and 26% vs. 10% of intestines). These data suggest that S. Enteritidis infections introduced into flocks during the later stages of pullet rearing have greater potential to persist into the early phase of egg production.