Producer question: E.coli has gotten much of the food safety attention, but is close behind. What should I know about on-farm control?

Blaha’s response: The increase of free trade and the decrease in consumers’ trust in the safety of food of animal origin have increased the interest in control programs to reduce the so-called zoonotic Salmonella species in the pork chain. This includes at the farm level.

“Zoonotic” microbes are pathogens that are transmissible from animals to man, which often do not cause disease in the animals, but can do so in man. This is true for most Salmonella species.

Major reasons for the increasing need for Salmonella control in pork are:

1. Pork is generally recognized, following poultry meat and eggs, as the second important source of human foodborne disease due to zoonotic Salmonella.

2. An outbreak of human salmonellosis caused by Salmonella infantis in 1993 in Copenhagen, Denmark, with more than 1,000 people hospitalized, was traced back to pork. This triggered the Danish National Salmonella Control in Pork Program. It has created market pressure in the pork export arena and also influences domestic markets.

3. The successful Salmonella control programs in Sweden, Finland and Norway during the past three to four decades became a political issue when Sweden and Finland joined the European Union in 1995. The herd/flock Salmonella prevalence in these countries is less than
1 percent, which is significantly lower than any other country.

4. Implementing a consistent program to control Salmonella in pork from “farm to table” would improve both the consumers’ trust in pork and long-term export market accessibility.

In early research into the occurrence of zoonotic Salmonella in swine (which is different from the porcine salmonellosis caused by Salmonella choleraesuis), researchers expected to identify a single pattern typical of Salmonella infection in swine. However, the idea of identifying a simple infection pattern common to zoonotic Salmonella in herds is fading away.

In-depth investigations reveal that the occurrence of zoonotic Salmonella is much more dynamic than once thought. Prevalence patterns are changing from farm to farm, from shipment to shipment and within a farm even over time, due to varying environmental conditions.

There is growing knowledge about the role of animal movement, environmental contamination, various Salmonella infection sources, possible reservoirs and daily work procedures for introducing Salmonella onto a farm and into a herd. We also know more about the perpetuation of the infection-contamination-infection cycle on farms today.

There is no silver bullet that solves the problem. However, there are many encouraging results on what contributes to a reasonable on-farm Salmonella reduction. Together, these measures have the potential to permanently reduce the Salmonella burden of swine farms. These include:
Applying feeding and nutrition methods that reduce the multiplication of Salmonella in swine. For example, using feed from mills with Good Manufacturing Practices that focus on reducing the Salmonella contamination risk of the feed.

Cleaning and disinfecting buildings, with targeted cleaning and removal of potential reservoirs such as dust, before bringing new stock into a barn. Also, daily disposal of spilled feed.

Targeted intensification of external and internal biosecurity measures. For example, limit truck and people traffic, change clothes and boots between barns, rodent control and other related biosecurity protocols.

“Salmonella-reducing” production procedures such as one-way flow of personnel and animals, and separating the swine herd from other livestock species.

Potentially competitive exclusion flora, vaccination as well as probiotics and feed additives, that reduce the multiplication of Salmonella – such as organic acids.

It is necessary to develop rapid and economic methods to identify farm-specific Salmonella patterns in order to choose the appropriate reduction measures. In other words, every farm needs a customized Salmonella reduction plan dependent on the type of operation, daily work procedures and actual sources of introducing and perpetuating Salmonella.

Finally, it is important to emphasize:

1. Salmonella in pork is not a new or emerging problem, nor is it due to any wrong doing. Rather, it is an opportunity to adopt higher level of safety and quality standards that today the industry can afford to pursue.

2. A Salmonella-positive pig or herd does not automatically translate to Salmonella-adulterated pork. However, Salmonella-positive slaughter hogs increase the risk of contaminating edible tissue from Salmonella-positive gut contents and tonsils during processing.

3. The goal of any control program should not be eradication, but rather the move toward zero-risk of carrying Salmonella into the food chain via infected or contaminated animals.

Unlike control programs for hog cholera and pseudorabies that have resulted in eradication, on-farm Salmonella-control programs are likely to become part of permanent quality and safety assurance programs. Long-term, it will help you improve the marketability of your products.

Veterinarian Thomas Blaha, has held the Endowed Allen D. Leman Chair in Swine Health and Epidemiology at the University of Minnesota since 1996. He is on sabatical from the Hanover School of Veterinary Medicine in Hanover, Germany.