Scientists at the U.S. Department of Agriculture's Agricultural Research Service Poultry Microbiological Safety Research Unit, Russell Research Center, in cooperation with the University of Georgia’s Department of Poultry Science, have completed a study to compare the microbiological quality of eggs derived from either cages or two floor systems. Project #641 was funded by the U.S. Poultry & Egg Association.

Non-washed eggs produced by hens housed on shavings had slightly higher aerobic bacterial levels compared to eggs produced on slats. Both floor treatments had significantly higher bacterial levels than eggs produced in cages. Washing of eggs significantly reduced aerobic bacteria and coliforms. Moving hens from floor systems to cages reduced contamination. Following re-transfer back to floor systems, aerobic contamination of shells returned to previously higher levels.

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The study also evaluated the potential for horizontal transmission of Salmonella spp. by determining the prevalence rate in hens in the three systems. Hens on shavings yielded a value of 40%, 18% on slats and 15% in cages. The prevalence of Campylobacter spp. attained 43% on shavings compared to 36% on slats and 28% in cages. It is noted that campylobacteriosis is not an egg-borne disease since the organism is extremely sensitive to desiccation during storage and to decontamination by washing. There is no evidence that vertical transmission of Campylobacter spp. occurs among hens held for egg production, irrespective of housing system.