An assessment of soybeans and other vegetable proteins as source of Salmonella contamination in pig production.

Background: 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 spread by feed from two feed mills to 78 swine producing herds.

Methods: The 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 the Company (A) that produced the salmonella contaminated feed, were by the Chi. Square test compared to the results from all the other (B - E) feed producers registered in Sweden. Isolated serovars were compared to serovars from human cases of salmonellosis.

Results: Salmonella (28 serovars) was frequently isolated from imported consignments of soybean meal (14.6%) and rape seed meal (10.0%). Company A largely 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 A when compared to the mills of the other companies which largely were supplied by soybean meal from a crushing plant with a low risk for salmonella contamination. Also the level of feed mill contamination of salmonella was higher for feed mills belonging to Company A in comparison to the other companies before and also after heat treatment. Four (10.5%) of the 38 serovars isolated from feed ingredients (28) and feed mills (10) were on the EU 2007 top ten list of human cases of salmonellosis and all but eight (78.9%) on a 12 year list (1997-2008) of cases of human salmonellosis in Sweden.

Conclusions: 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. This is challenge for the EU - feed industry due to the fact that 98% of the use of soybean/meal, an essential feed ingredient, is imported from crushing plants of third countries usually with an unknown salmonella status.