Salmonella Control: The Dutch Experience

By Wayne Du - Pork Quality Assurance Program Lead/OMAFRA. This article looks at the Dutch salmonella control experience and research projects, summarising what can be learned.
calendar icon 2 November 2007
clock icon 4 minute read

Salmonella is a group of bacteria that can cause a disease called salmonellosis in both animals and humans. Salmonellosis is one of the major foodborne diseases around the world. Foods associated with salmonellosis humans range from vegetables, fruits, milk, eggs to meat including pork. Reducing salmonella contamination along the pork supply chain is one of the priorities in food safety around the world.

In 2005, the Netherlands started a monitoring program for salmonella in pigs. The monitoring program is an obligatory program and is carried out at both the farm level (finishing pigs) and at the slaughterhouse level.

Monitoring at the Farm Level

At the farm level, salmonella monitoring is based on testing blood samples for the presence of antibodies against salmonella. For farms producing more than 30 market hogs per year, 12 blood samples have to be collected each 4-months either on-farm or at the slaughterhouse. Samples then are tested by approved labs. When a total of 36 blood samples per farm (one year of monitoring testing) is reached, the farm is classified into one of the three salmonella categories. Category one means that a farm is not or low infected and category 3 means that a farm is heavily infected and needs to take measures for salmonella reduction. All 36 samples have the same weight. The scores of the previous 12 months determine the salmonella categories (Table 1, 2)

Salmonella Score Determination
Results per 4 month period (12 tests) Score
Less than 20% positive 1
20-40% positive 2
More than 40% positive 3

Salmonella Classification
Results (scores) per 12month period (36 tests) Farm Category
3 or 4 1
5, 6 or 7 2
8 or 9 3

Monitoring at the Slaughterhouse Level

At the slaughterhouse level, monitoring is based on both serological and bacteriological tests. Slaughterhouses that slaughter more than 150,000 hogs per year have to sample five carcasses per day (analyzed in the lab as one pooled sample). Slaughterhouses that slaughter between 10,000 to 150,000 hogs per year have to sample ten carcasses per week (individual samples). Samples are collected in the cooling room.

Results of the Monitoring Program

At the farm level, results from 2006 show that 73% of the herds were in category 1, 23% in category 2 and 4% in category 3. Farms in category 3 were advised to take measures for salmonella reduction. At the end of 2007, it will be discussed if these farms will be obligated to take measures.

At the slaughterhouse level, monitoring results from 2006 show that the average salmonella contamination of the carcasses in the Dutch slaughterhouses was 0.8%, which is far below the EU standard of 10%. Therefore, no additional control measures were required or obligated at the slaughterhouses. However, slaughterhouses with salmonella contamination prevalence over 0.8% are advised to take measures to control salmonella.


Based on the Dutch salmonella control experience and research projects here are their recommendations:
  • Put most of the salmonella control efforts into implementing measures to avoid contamination of carcasses during the slaughter. Contaminated slaughter equipment is the most important source of carcass contamination, therefore, equipment should be constructed in a way that is easy to clean, disinfect and without the possibility for bacteria to attach and multiply.
  • Avoid cross contamination of salmonella between different herds in the lairage (holding area) of the slaughterhouse.
  • Reduce the salmonella prevalence at the farm level. The reduction results achieved at the farm level can only be converted into carcass salmonella reduction at the slaughterhouse if the slaughter line equipment contamination and potential cross contamination in the lairage are addressed.
October 2007
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