Environmental contamination and horizontal transmission of Salmonella Enteritidis among experimentally infected layer pullets in indoor cage-free housing

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

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2025
Publication Date: 5/5/2025
Citation: Gast, R.K., Garcia, J.S., Guraya, R., Jones, D.R., Karcher, D.M. 2025. Environmental contamination and horizontal transmission of Salmonella Enteritidis among experimentally infected layer pullets in indoor cage-free housing. Poultry Science 104:105236.

Interpretive Summary: The bacterial pathogen Salmonella Enteritidis can cause food-borne human illness as a result of its ability to invade the internal organs of laying hens and then be deposited inside the edible interior contents of eggs. The commercial egg industry is currently experiencing a transition toward increased utilization of non-cage housing systems for hens in response to animal welfare concerns, but the consequences of this shift for animal health and food safety are uncertain. This study assessed S. Enteritidis contamination of the housing environment and the transmission of infection within groups of immature laying hens (pullets) housed in a cage-free system. In each of 3 trials, groups of pullets were housed in an isolation facility that simulated a cage-free barn with perches and nest boxes. A different proportion of birds were orally infected with S. Enteritidis in each trial: 1/3 in trial 1, 1/6 in trial 2, and 1/12 in trial 3. At intervals during the first 2 wk after inoculation, 5 types of environmental samples were collected in each room and tested for S. Enteritidis contamination. At the end of this period, samples of several internal organs were collected from uninoculated birds (exposed to S. Enteritidis only by contact with inoculated penmates) and cultured to detect infection. The frequencies of recovery of S. Enteritidis from both environmental samples and internal organs from contact-exposed pullets were greatest in groups where 1/3 of the birds were orally inoculated and least in groups where 1/12 were inoculated. Overall, composite samples of the wood shavings flooring substrate (“litter”) provided the highest recovery of S. Enteritidis and the lowest recovery came from drag swabs of the flooring substrate. These results suggest that a high frequency of environmental contamination may be an important contributor to the spread of S. Enteritidis infections among pullets in cage-free housing.

Technical Abstract: The persistence and transmission of the egg-associated pathogen Salmonella Enteritidis in laying flocks are significantly influenced by the poultry housing environment. The present study assessed environmental contamination and horizontal transmission of S. Enteritidis within groups of layer pullets in cage-free housing after infection just before the age of sexual maturity. In each of 3 trials, 144 pullets were transferred from a rearing facility at 15 wk of age and randomly distributed between 2 isolation rooms simulating commercial cage-free barns with perches and nest boxes (72 birds/room). One wk after placement in the containment facility, a proportion of the 72 pullets in each room were orally inoculated with S. Enteritidis: 1/3 in trial 1, 1/6 in trial 2, 1/12 in trial 3. At 2 wk post-inoculation in each trial, samples of liver, spleen, and intestinal tract were collected from 40 uninoculated (contact-exposed) birds in each room for bacteriologic culturing to detect horizontal transmission of S. Enteritidis. At 6 intervals between inoculation and necropsy, 5 types of environmental samples (wall dust swab, nest box swab, perch swab, flooring substrate drag swab, and flooring substrate composite) were collected and cultured for S. Enteritidis. The overall frequencies of S. Enteritidis recovery from both environmental samples and internal organ from contact-exposed pullets after initial oral inoculation of 1/3 of the birds in each room (96.7% and 75.4%, respectively) were significantly greater than after initial infection of 1/6 of the birds (77.5% and 58.3%), and further significant decreases in S. Enteritidis recovery were observed for birds inoculated at a 1/12 proportion (10.0% of environmental samples and 17.9% of organs). Flooring substrate composites were the most efficient environmental sample type for all 3 trials combined (72.2% positive), providing significantly better S. Enteritidis recovery than the least efficient samples (flooring substrate drag swabs; 52.8% positive). These data suggest that a high frequency of environmental contamination may be an important contributor to horizontal transmission of S. Enteritidis infections among pullets in cage-free housing.