But USDA Agricultural Research Service (ARS) and Iowa State University (ISU) research shows this respite can significantly increase the pigs' chance of being exposed to Salmonella bacteria.
"We found up to a 10-fold increase in the number of pigs that tested positive for Salmonella infection at slaughter versus those tested on the farm," said ARS veterinary epidemiologist H. Scott Hurd.
The findings reveal that on-farm infection rates generally range from 4 to 7 per cent. "But we've found that the rate of infection among the pigs increases to nearly 40 per cent once they've spent just a few hours in the holding pen," he said. "This phenomenon is occurring in both large and small processing plants."
Most of the investigations needed to be carried out on farms and packing plants, and Hurd was happy with the level of cooperation he found within the industry. "That's unique within animal disease research," said Hurd. "We were right there, working with the producers and packers."
One of the investigations showed infection occurring in as little as one-half hour of exposure. In another, all hogs were contaminated after 6 hours of exposure. "The significance of this is that it's a newly recognised control point," he said. "The question is: what can be done about it?"
Hurd believes that moisture in the holding pens, coupled with the pigs' inherent nature to explore their new surroundings by roaming and snorting around, are the likely culprits that increase the rate of Salmonella exposure. While there is not much that can be done about the pigs' inquisitive nature, Hurd sees limiting moisture in the holding pens as one of the keys to reducing the infection rate.
One way of accomplishing this is by replacing the concrete floors now common in holding pens with slatted ones. This would allow for channelling most of the slurry in the pens off into pits. Without the slurry, there are fewer organisms to pick up.
Another way is to find an alternative to cooling the animals off with sprinklers. Cleaning and disinfecting the holding pens between occupancy by groups of pigs might also be effective. The scientists also studied a dietary solution: fructooligosaccharide (FOS), a nondigestible, soluble-fibre carbohydrate that supports growth of beneficial bacteria.
Hurd believes that pork processors already keep most Salmonella from reaching consumers. "A lot of Salmonella is cleaned up along the way," he said. "But anything that will further diminish the chances of foodborne contamination is a great boon. Making pork safer will attract health-conscious consumers in the United States and in foreign markets."