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

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

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2017
Publication Date: 10/1/2017
Citation: Gast, R.K., Guraya, R., Jones, D.R., Guard, J.Y., Anderson, K.E., Karcher, D.M. 2017. Frequency and duration of fecal shedding of Salmonella serovars Heidelberg and Typhimurium by experimentally infected laying hens housed in enriched colony cages at different stocking densities. Avian Diseases. 61:366-371.

Interpretive Summary: Eggs contaminated with Salmonella (particularly serovars Enteritidis, Heidelberg, and Typimurium) are important sources of human illness. Infected hens can lay eggs with these pathogenic bacteria on the outside of the shell or inside the edible yolk and albumen. 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 Salmonella 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. Heidelberg or S. Typhimurium 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. Heidelberg in their feces for 8 weeks after infection, but S. Typhimurium shedding ceased earlier. Likewise, hens in all types of cages shed S. Heidelberg in their feces at a higher overall frequency than S. Typhimurium. Housing did not influence the frequency of S. Typhimurium shedding, but hens in both higher stocking density cage groups (enriched colony and conventional) shed S. Heidelberg at a greater frequency than did hens in enriched colony cages at the lower density. These results demonstrate that stocking density can influence the fecal shedding of Salmonella by laying hens for some (but not all) serovars or strains.

Technical Abstract: Eggs contaminated with Salmonella Enteritidis are leading sources of human salmonellosis, but S. Heidelberg and S. Typhimurium are also egg-associated pathogens. The management practices and housing facilities characterizing different systems for housing commercial egg flocks can influence Salmonella persistence and transmission. Although animal welfare aspects of poultry housing have been widely debated, the food safety ramifications are not thoroughly understood. The present study assessed the effects of 2 different bird stocking densities on the frequency and persistence of fecal shedding of strains of S. Heidelberg and S. Typhimurium in groups of experimentally infected laying hens housed in colony cages enriched with perching and nesting areas. In separate trials, groups of laying hens were distributed at two stocking densities (648 and 973 sq. cm/bird) into enriched colony cages and (along with a group housed in conventional cages at 648 sq. cm/bird) orally inoculated with doses of 10e8 cfu of 2-strain cocktails of either S. Heidelberg or S. Typhimurium. At 8 weekly post-inoculation intervals, samples of voided feces were collected from beneath each cage and cultured to detect Salmonella. Fecal shedding of S. Heidelberg continued for 8 wk in all housing groups, but S. Typhimurium shedding ceased after as little as 5 wk (in enriched cages/low stocking density). Following S. Heidelberg infection, the overall frequency of positive fecal cultures for all sampling dates combined was significantly (P < 0.05) greater from either conventional cages (51.0%) or enriched cages/high stocking density (46.5%) than from enriched cages/low stocking density (33.3%). No significant differences in S. Typhimurium fecal isolation were identified between housing groups. The overall frequency of S. Heidelberg fecal recovery was significantly greater than the corresponding frequency of S. Typhimurium recovery from conventional cages (51.0% vs. 29.5%), enriched cages/high stocking density (46.5% vs. 25.3%), and enriched cages/low stocking density (33.0% vs. 22.2%). These results demonstrate that stocking density can affect intestinal colonization and fecal shedding in laying hens for some (but not necessarily all) Salmonella serovars or strains.