Frequency and duration of fecal shedding of Salmonella Enteritidis by experimentally infected laying hens housed in enriched colony cages at different stocking densities.

Authors: Gast, Richard; Guraya, Rupinder - Rupa; Jones, Deana; ANDERSON, KENNETH - North Carolina State University; KARCHER, DARRIN - Purdue University

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2017
Publication Date: 4/10/2017
Citation: Gast, R.K., Guraya, R., Jones, D.R., Anderson, K.E., Karcher, D.M. 2017. Frequency and durationn of fecal shedding of Salmonella Enteritidis by experimentally infected laying hens housed in enriched colony cages at different stocking densities. Frontiers in Veterinary Science. 4:47.

Interpretive Summary: The contamination of eggs with Salmonella Enteritidis has been implicated as an important cause of human illness. Infected hens can deposit these pathogenic bacteria inside the edible yolk or albumen of eggs before they are laid. In recent years, alternatives to conventional cage-based housing for poultry flocks have become increasingly common in the commercial egg industry, but the impact of different housing systems on S. Enteritidis infection and egg contamination are not yet fully understood. The present study assessed some of the potential effects of housing laying hens in colony cages, enriched with perches and enclosed nesting areas, at two different two different stocking densities (defined by the amount of floor space available to each bird). Groups of hens were housed at two different stocking densities (and a third group was placed in conventional cages at the higher density). S. Enteritidis infection was initiated by oral inoculation and samples of voided feces were then collected from each group at weekly intervals and tested for the presence of the pathogen. Hens in all three housing groups shed S. Enteritidis in their feces for 10 weeks after infection. S. Enteritidis was isolated from fecal samples at a higher overall frequency from hens in conventional cages than from hens in enriched colony cages at either stocking density. Moreover, the frequency of S. Enteritidis isolation from feces was significantly higher when infected hens were housed in enriched colony cages at the higher stocking density in comparison to the lower density. These results demonstrate that hen stocking density can affect the susceptibility of hens to intestinal colonization by S. Enteritidis, but that some other characteristic which distinguishes conventional and enriched colony cage systems may also exert an influence.

Technical Abstract: Human infections with Salmonella Enteritidis are often attributed to the consumption of contaminated eggs, so the prevalence of this pathogen in egg-laying poultry is an important public health risk factor. Numerous and complex environmental influences on Salmonella persistence and transmission are exerted by management practices and housing facilities used in commercial egg production. In recent years, the animal welfare implications of poultry housing systems have guided the development of alternatives to traditional cage-based housing, but their food safety consequences are not yet fully understood. The present study assessed the effects of different bird stocking densities on the frequency and persistence of fecal shedding of S. Enteritidis in groups of experimentally infected laying hens housed in colony cages enriched with perching and nesting areas. In two trials, groups of laying hens were distributed at two stocking densities (648 and 973 cm2/bird) into enriched colony cages and (along with a group housed in conventional cages at 648 cm2/bird) orally inoculated with doses of 1.0 × 108 cfu of S. Enteritidis. At 10 weekly post-inoculation intervals, samples of voided feces were collected from beneath each cage and cultured to detect S. Enteritidis. Fecal shedding of S. Enteritidis was detected for up to 10 wk post-inoculation by hens in all three housing treatment groups. The overall frequency of positive fecal cultures was significantly (P < 0.05) greater from conventional cages than from enriched colony cages (at the lower stocking density) for the total of all sampling dates (45.0% vs. 33.3%) and also for samples collected at 4-9 wk post-infection. Likewise, the frequency of S. Enteritidis isolation from feces from conventional cages was significantly greater than from enriched colony cages (at the higher hen stocking density) for the sum of all samples (45.0% vs. 36.7%) and at 6 wk post-inoculation. Moreover, the frequency of S. Enteritidis fecal recovery from enriched colony cages at the higher hen stocking was significantly greater than from similar cages at the lower stocking density for all 10 sampling dates combined (39.4% vs. 33.3%, P = 0.0185). These results suggest that stocking density can significantly affect S. Enteritidis intestinal colonization and fecal shedding in laying hens, but some other difference between conventional and enriched colony cage systems appears to exert an additional significant influence.