Farm Risk Factors for Salmonella Contamination of Eggs

An Iowa State University study indicates that adherence to a Salmonella vaccination programme and the elimination of infected rodents are the most effective measures to minimise the risk of Salmonella contamination of eggs from non-caged hens kept in small and medium-sized flocks.
calendar icon 29 June 2014
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Based on the initial findings in their study, Iowa State University researchers suggest the two most important risk factors for Salmonella Enteritidis contamination inside the bird area and in the eggs in small- and medium-sized flocks are the presence of infected rodents and the absence of an Salmonella Enteritidis vaccination programme.

Those are the conclusions of E.A. Wallner-Pendleton and co-authors of a paper about on-farm risk factors for Salmonella Enteritidis contamination, which they presented at a symposium on 'Reducing Salmonella Enteritidis Contamination of Shell Eggs with an Integrated Research and Outreach Approach'. The event was part of the Poultry Science Association’s annual meeting in San Diego, California in 2013 and the paper is published in the latest issue of Journal of Applied Poultry Research.

The researchers explain that 40 layer farms from two states participated in a study to examine the risk factors and incidence of Salmonella Enteritidis from multiple samples, including environmental drag swabs from the bird areas, feed, water, flies, rodents, live rodent traps and environmental swabs from areas occupied by other livestock.

Twenty-four of the farms had between 3,000 and 31,000 bird flocks (medium-sized flocks) and 16 had fewer than 3,000 birds (small-sized flocks). All were housed in cage-free production systems. Twenty-two farms included outside pasture areas for the birds.

Most of the participants had just come under the FDA Egg Rule and had not yet tested their flocks for Salmonella Enteritidis. (Flocks with less than 3,000 birds are exempt.) Many, however, obtained their pullets from commercial Salmonella Enteritidis-clean breeder sources hatched in National Poultry Improvement Plan hatcheries.

Vaccination against Salmonella Enteritidis was performed on 21 of the 40 farms (combination of live and killed vaccines).

Salmonella Enteritidis was detected on seven out of the 40 farms, primarily in rodents, their faeces, or from swabs taken inside live traps. Of these seven Salmonella Enteritidis-positive farms, three farms that had vaccinated their pullets with live Salmonella Typhimurium vaccine and killed-Salmonella Enteritidis vaccine; no Salmonella Enteritidis was isolated from the environmental drag swabs taken from the bird area or from the eggs on these farms.

However, on the farms that had not vaccinated for Salmonella Enteritidis, the organism was isolated from four environmental drag swabs and three egg pools. The last four farms had flocks of fewer than 3,000 birds.

No Salmonella Enteritidis was isolated from any of the samples of feed, flies, water or swabs taken from other livestock areas.


Wallner-Pendleton E.A., P.H. Patterson, S. Kariyawasam, D.W. Trampel and T. Denagamage. 2014. On-farm risk factors for Salmonella Enteritidis contamination. J. Appl. Poult. Res. 23(2): 345-352. doi: 10.3382/japr.2014-00943

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July 2014

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