Lairage, A Significant Source of Salmonell Contamination in Pork Chain

Salmonella is a significant food safety hazard of food and control of this organism will continue to be a challenge to the pork industry. Previous research shows that a higher Salmonella prevalence for pigs tested at slaughter, compared to when they are tested on farm. The stress of transportation and improper handling were blamed for causing this phenomenon. Stress has been suggested as a reason for increased Salmonella shedding and cross contamination between Salmonella-carrying and non-Salmonella carrying pigs. However, no studies have demonstrated a direct link between the increase in Salmonella shedding or infection and these physiological changes.

Recent studies at National Animal Disease Center (NADC) of the USDA demonstrated no difference between directly shipped pigs and those stressed by mixing, fasting and 18 hours lairage in a clean disinfected facility (Figure 1). These studies show that it is the lairage or holding pens that appear to be the primary source for Salmonella contamination in the pork chain. If this new finding is proved to be true it will have a significant impact on Salmonella reduction and prevention. Following are the key results summarized from the NADC studies.

• Lairages are a significant source for Salmonella contamination in the pork chain because results from the studies show:
  

  a) The number of Salmonella positive pigs were increased significantly after pigs stayed in holding pens;

b) More serotypes were isolated from pigs necropsied at the abattoir than were in pigs necropsied on farm.

• The increase of Salmonella positive pigs appears not due to the stress of animal transportation. There was no difference between directly shipped pigs and those stressed by mixing, fasting and 18 hour lairage in a clean disinfected facility.
  
• Rapid Salmonella infection is possible. Artificial infection trial showed that Salmonella negative pigs became infected in the ileocecal lymph nodes and gastrointestinal tract after only two hours of low dosage exposure to a Salmonella contaminated floor (80% of hogs became positive).

In summary, controlling Salmonella must take a systematic approach and a collective effort. All the segments along the pork chain from farm to fork must do their part.

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