Persistent Salmonella Enteritidis Environmental Contamination on Layer Farms

Research from Belgium has shown that Salmonella Enteritidis remains in the environment of persistently Salmonella Enteritidis-contaminated layer farms, even after cleaning and disinfection, despite obligatory vaccination. The scientists identified the egg-collecting area as a critical point of contamination on most farms.
calendar icon 20 February 2012
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The aim of a study reported by I. Dewaele of the Institute for Agricultural and Fisheries Research (ILVO) in Melle and co-authors there and at other research institutes across Belgium was to examine the Salmonella enterica serovar Enteritidis environmental contamination on persistently positive layer farms in Belgium during successive laying cycles.

In a paper published in Poultry Science, they explain that all of the farms were required to vaccinate their layers under the national control programme for Salmonella.

Seven farms with previous or current Salmonella Enteritidis contamination were monitored during different stages of the laying period and after cleaning and disinfection. Environmental samples, including from the equipment and vermin, were taken in the house and egg-collecting area. Dilutions were performed to define the degree of Salmonella Enteritidis contamination.

Eggshells, egg contents and caeca were also tested for Salmonella.

At the end of the first sampled laying period, 41.6 per cent of the environmental samples were contaminated with Salmonella Enteritidis. After cleaning and disinfection, the prevalence dropped to 11.4 per cent.

On average, the prevalence in the second laying period increased again: 17.8, 18.4, and 22.3 per cent at the onset, middle and end of the lay period, respectively. After cleaning and disinfection before the third laying period, the prevalence decreased to 6.6 per cent and stabilised at the onset of lay (6.3 per cent).

During lay, as well as after cleaning and disinfection, a wide variety of contaminated environmental samples were found; for example, in the hen–house, in the egg-collecting area, on mobile equipment and in or on vermin. In the hen–house during laying, the most recurrent and highly contaminated sites were the overshoes, floor, manure belt and hen faeces. The egg-collecting area had a significantly higher number of contaminated samples than the hen–house. For both sites, the floor appeared to be the most suitable sampling site to estimate the Salmonella Enteritidis status of the farms.

Eggshell and egg content contamination varied between 0.18 and 1.8 per cent and between 0.04 and 0.4 per cent, respectively. In total, 2.2 per cent of the analysed caeca contained Salmonella Enteritidis.

Dewaele and co-authors concluded that their study revealed Salmonella Enteritidis to be present in the environment of persistently Salmonella Enteritidis-contaminated layer farms. It also demonstrated that in many cases Salmonella Enteritidis contamination was not eliminated after cleaning and disinfection, and identified the egg-collecting area as a critical point on most farms.


Dewaele I., H. Van Meirhaeghe, G. Rasschaert, M. Vanrobaeys, E. De Graef, L. Herman, R. Ducatelle, M. Heyndrickx and K. De Reu. 2012. Persistent Salmonella Enteritidis environmental contamination on layer farms in the context of an implemented national control program with obligatory vaccination. Poult. Sci. 91(2):282-291. doi: 10.3382/ps.2011-01673

Further Reading

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February 2012
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