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Egg Bacterial Contamination Affected by Strain, Housing

24 September 2013

US - Experiments show that both hen strain and housing system impact the microbial levels on eggs.

A new study shows that hen strain has an effect on egg microbial levels for various housing systems, and egg safety should be considered when making hen strain selections for each housing system.

Deana Jones from the Egg Safety and Quality Research Unit, USDA Agricultural Research Service in Athens, Georgia, and K.E. Anderson of North Carolina State University have investigated how housing system and laying hen strain impact egg microbiology and food safety.

In the introduction to their paper in Poultry Science, they explain that alternative hen housing is becoming more commonplace in the egg market. However, a complete understanding of the implications for alternative housing systems on egg safety has not been achieved.

Their study examines the impact of housing Hy-Line Brown, Hy-Line Silver Brown and Barred Plymouth Rock hens in conventional cage, cage-free and free range egg production systems on shell microbiology.

Eggs were collected at four sampling periods. Egg shell emulsion pools were formed and enumerated for total aerobic organisms, Enterobacteriaceae, and yeast and mould counts.

Hy-Line Brown and Hy-Line Silver Brown hens produced eggs with significantly (P<0.05 and 0.001, respectively) different levels of aerobic organisms dependent on housing system. Eggs from conventional cages had significantly different (P<0.05) levels of aerobic contamination in relation to hen strain with Hy-Line Silver Brown having the greatest (4.57 log colony-forming units per millilitre).

Hy-Line Brown and Barred Plymouth Rock hens produced eggs with significantly different (P<0.01) levels of Enterobacteriaceae among housing systems, with conventional caged eggs having the lowest level of contamination for the hen strains.

There were no differences within each strain among housing systems for yeast and mould contamination.


Jones D.R. and K.E. Anderson. 2013. Housing system and laying hen strain impacts on egg microbiology. Poult. Sci. 92(8):2221-2225. doi: 10.3382/ps.2012-02799

Further Reading

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