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United States Department of Agriculture

Agricultural Research Service

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Research Project: MICROBIOLOGICAL COMPARISON OF TABLE EGGS HARVESTED FROM CAGED LEGHORN HENS AND CAGE-FREE FLOOR REARED LEGHORN HENS

Location: Poultry Microbiological Safety Research

2011 Annual Report


1a.Objectives (from AD-416)
Compare the microbiology of eggs obtained from caged Leghorn hens and cage-free floor housed Leghorn hens with both naturally contaminated and artificially inoculated environments.


1b.Approach (from AD-416)
Day of age Leghorn pullets will be obtained and reared in a confinement rearing facility set up to industry standards until the birds reach sexual maturity. At this time, a confinement housing facility would be set up to simulate a commercial Leghorn setting where the hens are housed in cages versus a confinement rearing facility where Leghorn hens are housed on the floor and eggs collected from nest boxes. To test the microbiology of the eggs from the two laying areas, an assortment of microbiological analyses (i.e. total aerobic plate count, Enterobacteriaceae count, E. coli count, Campylobacter, and Salmonella) of the eggs from both groups will be performed. In addition, another set of experiments will be conducted where the Leghorn hens are inoculated and colonized with a Naladixic acid resistant Salmonella and analysis of the eggs conducted.


3.Progress Report

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.

1. Non-washed eggs produced in a shavings covered floor environment had slightly higher aerobic bacteria levels (4.0 log / mL of rinsate) than eggs produced on slats (3.6 log), which had significantly higher bacteria levels than eggs produced in cages (3.1 log). Washing eggs significantly reduced aerobic bacteria level by 1.7 log and coliform count by 0.5 log. 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. 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 log. 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% of the hen density used in Experiment 1. Washing eggs further lowered aerobic bacteria levels to 0.4-0.7 log, 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 (compared to eggs 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 among hens on shavings covered floors (40%), while in the caged and slat housing systems Salmonella horizontal transmission was lower at 15 and 18%, respectively. The potential for horizontal transmission of Campylobacter (in an inoculated environment) was significantly greater among hens on the shavings covered floors (43%) than hens in the cages (28%) with hens on slats being intermediate (36%).


Last Modified: 8/1/2014
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