Colonization of internal organs by Salmonella serovars Heidelberg and Typhimurium in 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 - Michigan State University

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2016
Publication Date: 5/9/2017
Citation: Gast, R.K., Guraya, R., Jones, D.R., Guard, J.Y., Anderson, K.E., Karcher, D.M. 2017. Colonization of internal organs by Salmonella serovars Heidelberg and Typhimurium in experimentally infected laying hens housed in enriched colony cages at different stocking densities. Poultry Science. 96:1402-1409.

Interpretive Summary: Human illness has sometimes been caused by the consumption of eggs contaminated with Salmonella serovars Heidelberg or Typhimurium. These bacterial pathogens can be deposited inside the edible yolk or albumen of eggs after infection spreads to the reproductive organs of laying hens. In recent years, there has been growing interest in alternatives to conventional caged housing for egg-laying flocks to improve animal welfare, but the food safety consequences of the various poultry housing systems have not been fully established. 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 stocking densities (defined by the amount of floor space available to each bird). Another group of hens was placed in conventional cages at the higher stocking density. All hens were infected by oral inoculation (with S. Heidelberg in one trial and S. Typhimurium in the other) and the birds were euthanized the following week so tissues samples could be collected and tested for bacterial colonization. S. Heidelberg was found significantly more often in the ceca of hens than was S. Typhimurium, but the opposite was true for samples of livers and spleens. However, there were no differences between any of the housing systems or stocking densities in the isolation of either Salmonella strain from tissues. These results, which differ from a prior similar study using Salmonella serovar Enteritidis, demonstrate that the effects of housing systems on parameters important to food safety may sometimes vary between different pathogenic microorganisms.

Technical Abstract: Contaminated eggs produced by infected commercial laying flocks are often implicated as sources of human infections with Salmonella Enteritidis, but Salmonella serovars Heidelberg and Typhimurium have also been associated with egg-transmitted illness. Contamination of the edible contents of eggs is a consequence of the colonization of reproductive tissues in systemically infected hens. In recent years, the animal welfare implications of diverse poultry housing and management systems have been vigorously debated, but the food safety significance of laying hen housing remains uncertain. The present study evaluated the effects of two different bird stocking densities on the invasion of internal organs by Salmonella serovars Heidelberg and Typhimurium in groups of experimentally infected laying hens housed in colony cages enriched with perching and nesting areas. Laying hens were distributed at two different stocking densities (648 and 973 cm2/bird) into colony cages and (along with a group housed in conventional cages at 648 cm2/bird) orally inoculated with doses of 107 cfu of two-strain cocktails of either Salmonella Heidelberg or Salmonella Typhimurium. At 5-6 d post-inoculation, hens were euthanized and samples of internal organs (cecum, liver, spleen, ovary, and oviduct) were removed for bacteriologic culturing. The overall frequency of isolation of serovar Heidelberg from ceca (83.3%) was significantly (P < 0.001) greater than the corresponding value for serovar Typhimurium (53.8%). Conversely, serovar Typhimurium was recovered significantly more often from both livers (85.2% vs. 53.7%; P < 0.0001) and spleens (78.7% vs. 56.5%; P = 0.0008) than was serovar Heidelberg. However, there were no significant differences (P > 0.05) between stocking densities or cage systems in the frequencies of isolation of either Salmonella serovar from any of the five sampled tissues. These results contrast with prior studies which reported increased susceptibility to internal organ invasion by Salmonella Enteritidis among hens in conventional cages at higher stocking densities.