Food safety is a major issue these days — we all expect to eat wholesome foodfree of infectious pathogens, and hence, the production chain has to maintain and improve hygiene and other factors to ensure that the pork reaching the consumer is of the highest quality. Swine carry hundreds of strains of bacteria in their digestive tracts. Most of these are harmless to humans, but some are very harmful, such as certain Salmonellastrains, as they can be transferred to humans from swine.
Salmonella typhimuriumis one strain well-known to most of the population. Scare stories can do untold damage to our production sectors, as seen a few years ago when a U.K. government minister made comments about Salmonellaand poultry, given that salmonellosis can be fatal. A recent European Union zoonoses report stated that there were just over 160,000 reported cases of salmonellosis which included 50 fatal occurrences. About 60 percent to 70 percent were traced to contaminated meat, milk and eggs.
The biggest source of infection was poultry (accounting for 50 percent to 60 percent), with swine next (at 20 percent to 30 percent) and beef the lowest (from 1 percent to 20 percent). In 2003, the European Union set national targets of incidence, along with baselines which have to be lowered each year.
Denmark exports massive amounts of pigmeat — so the Danes focused on where they could gain an edge with their export business. They started checking for salmonellosis back in 1995, when approximately 1,100 people fell ill from Salmonellatraced to pork. Salmonellatesting started in 1998, initially with breeding and multiplier herds, but now for all herds.
If a pig becomes infected with Salmonella, its immune system starts to produce antibodies two to four weeks later. The antibody level is used as a quantitative indicator of Salmonella, using an ELISA test. The scheme was set up as shown below. Each swine herd is sorted into one of three classes, depending on the degree of Salmonellacontamination present:
Level 1:None or few seropositive samples = Not requiring action.
Level 2:A moderate number of seropositive samples = The herd owner has to contact a production advisor to develop a plan to reduce Salmonella. Swine fecal samples are taken to identify the Salmonellaserotype. (Same applies for Level 3 herds.)
Level 3:The number of positive samples is very high = The herd owner has to contact a production advisor, and all slaughter pigs must be slaughtered under increased hygienic conditions. This may entail having the pigs slaughtered at designated slaughter plants or at the end of a production run to prevent cross-contamination with other carcasses. All meat from Level 3 herds also has to be heat-treated or subjected to other special treatment. Strict financial penalties are imposed, so Level 3 herds get hit much harder than Level 2 or Level 1 herds.
Initially, meat samples (taken from one of three well-defined muscles) from 400,000 finishing pigs were tested on an annual basis following slaughter. In 2001, a new testing system was introduced based on USDA’s approach, as it was twice as sensitive as the initial Danish one.
The total cost of Danish Salmonellatesting stood at $6.5 million in 2005. Also, that year, Salmonellacases had fallen dramatically to 215.
Salmonellatesting of feeds has been in place for many years, and all compound feeds are heat-treated at 178° F to destroy Salmonellabacteria.
At the farm level, Salmonellacan be a tough cookie to eliminate. Initially the infection can occur through contaminated feed. Once in the hogs, transmission can move vertically from sows to piglets to weaners to finishers, as well as horizontally within pig groups by recontamination.
According to Professor Thomas Blaha, DVM, there is no general infection route; each herd has its own infection pattern. This means before taking action on a positive farm it’s necessary to identify the pattern and to concentrate on the infection “hot spots.” In herds showing high infection levels (Level 3), the first step is to test all pig age groups — sows, weaned pigs and so forth — as well as their environment. Secondly, identify how the infection is getting in — rodents, boots and such — as well as how the infection is re-circulating.
External biosecurity measures applied to minimize Salmonellaintroduction include showers for trucks and humans, “barn specific” boots and coveralls, rodent control and extensive bird netting of windows. Visitors must follow specific protocols as well.
Internal biosecurity measures such as changing boots between barns and rodent control are important. Moving pig flows from continuous systems to all-in/all-out will reduce the problem considerably, coupled with strict cleaning and disinfection protocols. Over-crowding hogs and mixing different age groups should also be avoided. Vaccination is another effective measure, Blaha contends.
As far as feed and additives are concerned, fermented liquid feeding, very common in Denmark, has been found to offer better protection against Salmonellacontamination than dry feed. Increasing the amount of barley (high fiber) in the diet has proved beneficial, as has grinding feed ingredients coarsely. Adding organic acids such as formic acid to feed and watering systems also reduces Salmonellaincidence. Potassium diformate (K-diformate) has a similar action and is also easier to handle than formic acid, Blaha notes.
The first critical stage to infection is when pathogens stick to the gut wall. However, when materials rich in mannose are included in the feed, the Salmonellabind to the mannose instead of the gut wall and are literally flushed out of the intestinal tract. Mannanoligosaccharides are more effective than free mannose in their binding capacity, and such extracts are available commercially. Trials on a U.K. farm found that mannanoligosaccharides included at a rate of 2 pounds per ton in the feed effectively reduced Salmonella-positive meat-juice samples, when a strict cleaning and hygiene program had proved ineffective, Blaha notes.
In Denmark, pigs cannot be fed less than 12 hours before slaughter (but must have access to water). That’s because removing a full stomach increases the risk of perforation and contamination. Other reduction measures include cleaning all equipment in water heated to 180° F.
Food safety is a very topical issue with any food scares quickly making headlines. One problem is that food poisoning outbreaks can be wrongly attributed to “contaminated” meat, including pork, when so many other handling practices can be to blame. Danish producers candidly admit their frustration both in terms of production and animal welfare in trying to follow Salmonella-free protocols. Regardless, for countries that rely on pork exports, an extensive Salmonellatesting program is part of the real world.
Food scares seem to be an ever-increasing reality in our world. As a kid, I ate dirt and worms in our backyard and my gut flora adjusted accordingly.
Today, kids, certainly in the United Kingdom, rarely get to grovel in the dirt, as young moms consider it “unhealthy” and the kids stay indoors glued to the TV or computer. Maybe those trendy moms need a re-education program as well.