Newswise — Looking for ways to keep market-bound swine as free of Salmonella as possible, researchers have come back to what most suspected in the first place: follow principles of sanitation on the farm, keep the transport vehicles clean, maintain sanitation in processing companies' abattoirs, watch out for dirty water and handle the carcasses carefully.

"Intervention at just one point is probably not going to be sufficient," explained Ron Griffith, a Food Safety Consortium researcher in veterinary microbiology at Iowa State University. "It does no good to have clean pigs on the farm and run them into a dirty abattoir. And it does no good to have dirty pigs on a farm and run them into a clean abattoir."

Griffith and his co-workers Jim McKean and Scott Hurd noted these principles after examining whether there would be any benefit to shortening the time that swine spend in holding pens and expose themselves to Salmonella contamination. He found that it wouldn't be possible to shorten that time span enough to make a difference. In a few cases, pigs could be infected after 15 minutes in the pen.

Most facilities hold pigs in the pen for at least two hours, Griffith said. Studies have shown that pigs held in the pens for two, four or six hours tested positive for Salmonella, with higher rates for those held longer.

"The work we've been involved with is trying to reduce the Salmonella in that abattoir holding area," Griffith said. "If that could be accomplished, pigs could go into a clean abattoir unit and possibly reduce the amount of Salmonella."

In the process, pigs are taken to a pen for holding and then taken to slaughter. Then another group of pigs comes into the pen, with several groups of pigs taking their turn in the pen during a day. At best, it may be flushed with water between groups but it's likely not clean, Griffith said. In some studies, each pen showed evidence of Salmonella.

"Until now we really hadn't had good evidence that the abattoir holding had an effect," he said. "Many people were saying that the pigs were picking it up in transit and that stress was a major factor."

In that case, the answer may be to go back to the farm. The ideal would be to never let a pig with Salmonella leave the farm and come to the abattoir, but that would be difficult to achieve, Griffith noted.

In Denmark, pork producers follow stringent procedures at the farm level to limit Salmonella exposure. The American model, Griffith said, has been to increase sanitation at the processing level and to pay attention to the critical control points in the plants. The American plan has its merits because the processing plant is where Salmonella activity is likely to pick up.

"If you go out to an ordinary pig farm and examine resting pigs " not excited, not moved " and do fecal cultures on them, you're going to get from 1 to 3 percent of them Salmonella positive. If you take the same pigs and sample their intestines at the slaughter plant, you can have up to 70 or 80 percent positive."