Study Finds Salmonella-Contaminated Feed Ingredients

SWEDEN - Salmonella was isolated from 15 per cent of soybean meal consignments, 10 per cent of rapeseed meal samples and up to 13 per cent of finished feed from five feed mills, representing a significant source of these bacteria on pig farms.
calendar icon 22 February 2010
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M. Wierup of Swedish University of Agricultural Sciences in Uppsala and P. Häggblom of the National Veterinary Institute in the same city have published their assessment of soybeans and other vegetable proteins as source of salmonella contamination in pig production in the journal, Acta Veterinaria Scandinavica.

The impact of salmonella-contaminated feed ingredients on the risk for spreading salmonella to pigs was assessed in response to two incidences when salmonella was known to have been spread by feed from two feed mills to 78 pig herds, explained Wierup and Häggblom.

Their assessment was based on results from the salmonella surveillance of feed ingredients before introduction to feed mills and from HACCP-based surveillance of the feed mills. Results from the mills of one company (Company A) that produced the salmonella-contaminated feed, were by the chi-square test compared to the results from all the other four companies (B-E), feed producers registered in Sweden. Isolated serovars were compared to serovars from human cases of salmonellosis.


Salmonella (28 serovars) was frequently isolated from imported consignments of soybean meal (14.6 per cent) and rape seed meal (10.0 per cent). Nine per cent of the corn samples and 0.9 per cent of the palm kernel samples were found to be positive for Salmonella.

Company A mainly imported soybean meal from crushing plants with a history of unknown or frequent salmonella contamination. The risk for consignments of vegetable proteins to be salmonella contaminated was 2.4 times (P<0.0006) larger for company A than the other mills, which generally sourced soybean meal from a crushing plant with a low risk for salmonella contamination.

The level of feed mill contamination with salmonella was also higher for feed mills belonging to company A (13.3 per cent) than the other companies (2.6 to 9.5 per cent), even after heat treatment.

Four (10.5 per cent) of the 38 serovars isolated from feed ingredients (28) and feed mills (10) were on the EU 2007 top ten list as causes of salmonellosis in humans. These were S. Agona, S. Infantis, S. Kentucky and S. Typhimurium. Furthermore, 30 of the serovars (78.9 per cent) found are on a 12-year list (1997-2008) of causes of human salmonellosis in Sweden.


Wierup and Häggblom concluded that Salmonella-contaminated feed ingredients are an important source for introducing salmonella into the feed and food chain.

Effective HACCP-based control and associated corrective actions are required to prevent salmonella contamination of feed.

Efforts should be taken to prevent salmonella contamination already at the crushing plants.

The researchers pointed out that this is challenge for the EU feed industry as 98 per cent of the soybean meal is imported from crushing plants in third countries and usually with an unknown salmonella status.


Wierup M. and P. Häggblom. 2010. An assessment of soybeans and other vegetable proteins as source of salmonella contamination in pig production. Acta Veterinaria Scandinavica, 52:15 doi:10.1186/1751-0147-52-15.

Further Reading

- You can view the provisional PDF version of the full report by clicking here.
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