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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Egg Safety & Quality Research » Research » Research Project #430344

Research Project: Evaluation of Management of Laying Hens and Housing Systems to Control Salmonella and Other Pathogenic Infections, Egg Contamination, and Product Quality

Location: Egg Safety & Quality Research

2018 Annual Report


1a. Objectives (from AD-416):
Objective 1: Assess the impact of dietary regimens, housing systems, and different chicken genetic lines on Salmonella (S.) infections of hens, Salmonella contamination of the production environment and eggs, and physical and functional egg quality. 1.a. Holistic comparison of genetic strains in commercial cage-free aviary housing. 1.b. Compare Salmonella shedding and microbial quality of eggs and environment in commercial-style conventional cage, enriched colony cage, enrichable colony cage, cage-free, and free range systems for various genetic strains of laying hens. 1.c. Assess the susceptibility of defined genetic lines of laying hens to infection with S. Enteritidis when housed in different cage-based production systems. Objective 2: Assess the effects of key management practices using experimental and field models of different housing systems on hen health, microbial ecology of foodborne bacteria, and antimicrobial resistance associated with egg contamination. 2.a. Assess the effects of different stocking densities on S. Enteritidis infections in laying hens housed in enriched colony cages. 2.b. Assess the effects of different cage-based housing systems on infections of laying hens with Salmonella serotypes (other than Enteritidis) which are significantly associated with egg contamination. 2.c. Determine the impact of hen housing systems on prevalence, diversity, and antimicrobial resistance of Salmonella, Campylobacter, Listeria, and Enterobacteriaceae associated with the production environment and eggs.


1b. Approach (from AD-416):
The housing of laying hens has become a matter of state and federal regulatory concern, as well as a purchasing consideration for consumers. While the shift in European Union laying hen housing requirements resulted in a plethora of research, most have limited similarity to the management systems utilized in the U.S. This project will, through national collaborative efforts, examine the impact of U.S. commercial hen housing systems on hen health and well-being, egg and environmental microbiology, and Salmonella infection and transmission. The collaborations associated with this project allow for a comprehensive examination of hen housing systems in a cost-effective manner. Furthermore, the project incorporates the research gaps identified by federal and state regulatory groups, as well as large and small egg producers. The research project will determine the impact of hen housing systems and laying hen genetic strain on the prevalence of Salmonella, as well as other human pathogens. Additionally, this project will determine the infection rate and transmission of various Salmonella strains within these housing systems. The effects of housing and management strategies on egg quality will also be assessed. The data generated from the project can be utilized by large and small egg producers to develop informed production management plans and state and federal regulatory groups to determine regulatory needs to ensure safe, high quality eggs reach consumers.


3. Progress Report:
Influence of genetic strain and housing system on egg and environmental microbiology. A study was concluded assessing the impact of 4 hen housing systems and 3 genetic strains of laying hens on egg and environmental microbiology. Samples were collected every 8 wk from a collaborative commercial style research farm. Indicator populations (total aerobes, Enterobacteriaceae, and yeasts and molds) were enumerated. Pathogen (Salmonella, Campylobacter, and Listeria) prevalence was also determined. The project was conducted from 20 – 68 wk of age. Influence of genetic strain and housing system on pathogen shedding. A study was conducted to determine the impact of 4 housing systems and 3 genetic strains of laying hens on Salmonella, Campylobacter, and Listeria shedding. Beginning at hatch, fecal samples were collected monthly and assessed for pathogen prevalence. The assessment was conducted from hatch – 68 wk of age. Deposition of Salmonella Enteritidis inside eggs produced by commercial genetic lines of laying hens housed in conventional cages or enriched colonies. A study to determine the frequency at which this epidemiologically important Salmonella serovar was deposited in the edible contents of eggs laid by experimentally infected hens representing four genetically distinct commercial lines (in two different housing systems) was completed. Egg physical quality across hen housing systems and genetic strains. A study was completed to assess the impact of 4 hen housing systems and 3 genetic strains of laying hens on egg physical quality parameters. Bi-monthly egg samples were evaluated for egg shape, shell characteristics, interior quality, and yolk physical characteristics. This study was conducted from 20 – 68 wk of age. Hen housing system influence on egg functional quality. A study was completed examining the influence of hen housing system on functional characteristics of eggs. Eggs from a single genetic brown egg strain of laying hen were collected bi-monthly and assessed for foaming, emulsification, and coagulation functions in food matrices. Consumer quality traits were also compared. The study was conducted from 20 – 68 wk of age. Effectiveness of manure drag swab pooling on the detection of Salmonella spp. A study was concluded to determine the effectiveness of various pooling scheme on the effective detection of Salmonella spp. in federally required manure drag swab samples in laying hen barns. This study was conducted in conjunction with the Food and Drug Administration.


4. Accomplishments
1. Egg processing and storage conditions impact on egg physical quality during extended storage. The international trade of shell eggs has become more important in recent years in order to feed a growing worldwide population, meet food manufacturing demands, and address supply issues during disease outbreaks or product recalls. The primary barriers for the export and import of shell eggs are: whether to wash eggs and egg storage temperature. ARS researchers at Athens, Georgia, undertook a study to compare egg quality factors as influenced by egg washing and storage temperature. Three lots of nest run (unwashed) white shell eggs were collected on consecutive days from a commercial in-line egg production facility. The treatment and storage conditions were selected to encompass the primary egg handling and storage conditions utilized throughout the world: washed; washed, oiled; and unwashed stored at 4°C; and unwashed stored at 22°C. Eggs were assessed weekly from 0 – 15 wk. Percent egg weight loss was greatest for the unwashed 22°C eggs (15.72 %) and least for washed, oiled 4°C (0.33 %). Less than 24 h at 22°C had a greater impact on yolk shape measurements decline than 15 wk at 4°C. After 15 wk, average Haugh unit scores (objective egg grade assessment) for all refrigerated treatments were still Grade A, unwashed 22°C dropped from Grade AA to almost Grade B in 1 wk. Room temperature storage of eggs rapidly declines egg quality. All refrigerated treatments maintained similar levels of egg quality throughout storage. Washing and oiling eggs before refrigerated storage did suppress the rate of egg weight loss. Maintaining eggs at refrigerated temperature has the greatest impact on maintaining egg quality, whether or not eggs were washed before entering refrigeration.

2. Invasion of internal organs by Salmonella Enteritidis in commercial genetic lines of laying hens housed in conventional cages or enriched colonies. The transmission of S. Enteritidis to humans inside contaminated eggs laid by infected hens is a leading public health concern, but the effects of different poultry housing systems on the microbial safety of eggs produced by different genetic lines of chickens are not fully understood. ARS researchers at Athens, Georgia, assessed the invasion of internal organs by S. Enteritidis in groups of experimentally infected laying hens of four commercial genetic lines (two brown egg and two white egg lines), housed in both conventional cages and colony units enriched with access to perches and nesting areas. All hens were orally inoculated with S. Enteritidis and samples of liver, spleen, ovary, oviduct, and intestinal tract were removed from euthanized hens for bacteriologic culturing one week later. S. Enteritidis was recovered from intestinal samples at a significantly higher frequency from the white egg lines than from the brown egg lines in both conventional cage and enriched colony housing systems. For one brown egg line, the frequency of intestinal S. Enteritidis recovery was greater in conventional cages than in enriched colonies. However, there were no significant differences between hen lines or housing systems in S. Enteritidis isolation from any other internal organs. These results demonstrate that colonization of the intestinal tract by S. Enteritidis sometimes varies between genetic lines of egg-laying hens and that different housing systems can affect this colonization for some lines.

3. Survival and multiplication of genetically characterized Salmonella Enteritis strains in egg yolk and albumen. The survival and growth of S. Enteritidis strains in the edible contents of contaminated eggs plays such a major role in causing human illness that prompt refrigeration of eggs to prevent bacterial multiplication has been identified as the most important risk reduction practice to protect consumers. ARS researchers at Athens, Georgia, compared the abilities of ten S. Enteritidis strains, each of which had been previously characterized for several significant genetic and cellular characteristics, to grow rapidly in egg yolk and to survive for several days in egg albumen during storage at 25° C. Very small numbers of S. Enteritidis cells multiplied to levels more than 10 million times greater by 24 hours of incubation and larger numbers of S. Enteritidis cells remained at nearly constant levels in albumen through 96 hours of incubation, with relatively little overall variation observed between strains after incubation in either yolk or albumen. However, significant differences that were detected between individual strains suggested that possessing a gene that coded for fimbrial protein structures on the bacterial cell surface may have been useful for growth inside egg yolk, whereas maintaining a gene that coded for antibiotic resistance may have reduced bacterial survival in egg albumen. These results demonstrate that a few defined genetic characteristics of S. Enteritidis strains can affect their survival and growth properties in eggs, but the extent of variation between strains is likely insufficient to influence the effectiveness of egg refrigeration.


Review Publications
Gast, R.K., Waltman, D.W. 2018. Salmonellosis. Diagnosis of major poultry diseases. Y.J. Saif and H. Toro, eds.pp. 55-59. Servet Publishing, Zaragoza, Spain.

Chousalker, K., Gast, R.K., Martelli, F., Soboleva, T., Pande, V. 2018. Review of egg-related salmonellosis and reduction strategies. Critical Reviews in Microbiology. 44:290-293.

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.

Jones, D.R., Ward, G.E., Regmi, P., Karcher, D.M. 2018. Impact of egg handling and conditions during extended storage on egg quality. Poultry Science. 97:716-723.

Gast, R.K., Guard, J.Y., Guraya, R., Locatelli, A. 2018. Multiplication in egg yolk and survival in egg albumen of genetically and phenotypically characterized Salmonella Enteritidis strains. Journal of Food Protection. 81:876-880.

Jones, D.R., Karcher, D., Regmi, P., Robison, C.O., Gast, R.K. 2018. Hen genetic strain and extended cold storage implications on physical egg quality from cage-free aviary housing system. Poultry Science. 97: 2347-2355.