Quick Analysis of Transport Can Save Problems at Processing Plants

The slaughterhouse’s holding pen – known also as lairage – is the end of the line for hogs on their way through the food chain. It can also be the beginning of the line for the spread of pathogenic Salmonella if processors don’t take note of whether incoming hogs are bringing the bacteria with them or developing it at the lairage.

The key is finding out early enough in the process at the lairage. That has led Food Safety Consortium researchers at Iowa State University to look for a way to determine within a few hours whether transport vehicles or lairage facilities have a minimal infective dose of Salmonella.

They are trying to do so by using a polymerase chain reaction (PCR), a technique for amplifying specific fragments of DNA sequences for ready laboratory analysis.

“We can get a sample in and we use our PCR kit on it,” explained Stephen Gaul, an ISU researcher who assisted D.L. (Hank) Harris, professor of animal sciences. “It takes about two hours to do the extractions, depending on how many samples we do at one time. Then running the PCR is another four hours.”

About six hours after the sample was obtained, Gaul said, “you’d know if it’s positive for Salmonella and, hopefully, with the standard controls in there you can find out exactly how much there is in that fecal sample.”

Once the results would be known, lairage operators would have time to implement sanitation procedures that would bring any Salmonella infection levels down
to minimal level, if necessary.

Few studies have been conducted in transport vehicles to determine whether current steps are sufficiently reducing infectious diseases in pigs. Those that have been done indicated that the level of Salmonella in cleaned and disinfected transport vehicles is below the level necessary to infect pigs.

The ISU study concentrated on the slaughter plants’ holding pens. Preliminary samples of pens in one slaughter plant suggested that the plant’s procedures reduced the transmission of Salmonella between different groups of incoming pigs. That could result in a reduction of contaminated carcasses.

Subsequent work will seek to find out if samples from another slaughter plant show effective results in reducing Salmonella in its holding pens. Those samples would be compared with the results from the first plant to help make the determination.