A study involving a microbiological comparison of eggs from cages versus floor-housed hens was carried out by Drs R.J. Buhr and N.A. Cox of the USDA Agricultural Research Service's Russell Research Center in Athens, Georgia as well as Dr J.L. Wilson and J.F. Hannah of the University of Georgia. Their work was sponsored by the US Poultry & Egg Association.

The researchers explain that fast-food restaurants have requested the poultry industry to supply a certain percentage of table eggs from hens maintained on floor environments (cage-free) instead of colony cage environments due to animal welfare concerns. Industry scientists have requested comparisons of the microbiology of table eggs obtained from laying hens housed in cages versus hens housed on the floor. Research information is needed to determine whether it is appropriate to comply with or rebut these requests from a food safety, microbiological and egg sanitation standpoint.

The objective of this study was to compare the microbiology of eggs obtained from both caged laying hens and cage-free floor housed hens in naturally contaminated and artificially inoculated environments.

In Experiment 1, non-washed eggs produced in a shavings covered floor environment had slightly higher aerobic bacteria levels (APC 4.0 log₁₀cfu/mL of rinsate) than eggs produced on slats (APC 3.6 log₁₀cfu/mL), which had significantly higher bacteria levels than eggs produced in cages (APC 3.1 log₁₀cfu/mL). Washing eggs significantly reduced aerobic bacteria level by 1.7 log₁₀cfu/mL and coliform count by 0.5 log₁₀cfu/mL. No significant differences were found in aerobic bacteria, E. coli and coliform counts on eggs from the three housing system types after the eggs were washed.

In Experiment 2, non-washed eggs produced by hens moved into triple-deck cages from 57 to 62 weeks (previously housed on shavings, slats and cages) did not differ in aerobic bacteria levels. Washing eggs continued to significantly reduce aerobic bacteria level to below 0.2 log₁₀cfu/mL.

In Experiment 3, the levels of aerobic bacteria for non-washed eggs were within 0.4-log below the aerobic bacteria values attained for non-washed eggs in Experiment 1, although hens in Experiment 3 were at 28 per cent of the hen density used in Experiment 1. Washing eggs further lowered aerobic bacteria levels to 0.4 to 0.7 log₁₀cfu/mL, a 2.7-log reduction.

These results indicate that eggshell bacteria levels are similar following washing eggs from hens housed in these cage and cage-free environments. However, housing hens in cages with manure removal belts resulted in lower aerobic bacteria levels for both non-washed and washed eggs than those from hens housed in a room with cages, slats and shavings.

The potential for horizontal transmission of Salmonella (in an inoculated environment) was significantly greater for hens on shavings covered floors (40 per cent), while in the caged and slat housing systems, Salmonella horizontal transmission was lower at 15 and 18 per cent, respectively. The potential for horizontal transmission of Campylobacter (in an inoculated environment) was significantly greater for hens on the shavings covered floors (43 per cent) than hens in the cages (28 per cent) with hens on slats being intermediate (36 per cent).

In summary, the researchers concluded that eggs produced by hens in cage-free environments that contain shavings had higher eggshell aerobic bacteria levels and was not influenced by housing density. However, following washing, aerobic bacteria levels did not differ for eggs from cage or cage-free housing systems. The potential for horizontal transmission of both Salmonella and Campylobacter (in an inoculated environments) was found to be greater among hens housed on shavings covered floors than among hens housed in cages or slat systems.

October 2010