USDA’s Food Safety and Inspection Service (FSIS) used to test only whole carcasses. In 2016, when it also started testing chicken parts separately, it became clear that when the chicken is cut, “it causes a bloom in the Salmonella,” Hofacre told Poultry Health Today.

S. Heidelberg challenge

To evaluate the effectiveness of vaccination, Hofacre led a floor-pen study. Investigators vaccinated all 1-day-old broilers in the hatchery. At 4 days of age, they administered S. Heidelberg to half of the birds in each pen, which then transmitted the pathogen to other pen mates. The vaccinated birds received a field boost in the water at 14 days.

The birds, which were processed at 42 days of age at a small plant run by the USDA’s Russell Research Center, were not eviscerated, but hocks were removed and a carcass rinse was then done.

Salmonella was then measured at three different points: in the pens, in the carcass rinse after processing and in the ceca, which was removed after processing, he continued.

Carcass-rinse results

Compared to the unvaccinated group, the carcass rinse from vaccinated birds contained 20 percent less Salmonella (31 percent versus 11 percent), Hofacre reported.

“They had less in their intestines, less in the environment and then less on that final carcass rinse in the processing plant,” he added. Vaccination lowered Salmonella during all three steps.

More companies in the US poultry industry are vaccinating broilers against Salmonella to maintain a favorable FSIS category or to move their results lower and into a better category. Vaccination against Salmonella, Hofacre said, is also being used by companies that are having issues with S. Enteritidis or S. Heidelberg, which pose a greater risk to human health.

Vaccination coupled with the chemical interventions used at processing can substantially reduce the level of Salmonella in the final product that goes to the consumer, Hofacre said.

However, he cautioned that reducing Salmonella should start with breeders so there will be less in the chicks when they’re hatched and less on the broiler farm, Hofacre noted.

“A breeder programme, no matter what you start with today, is going to take at least a year before it fully impacts [the incidence of Salmonella in broilers],” he said.

During that time, producers can use the live-vaccination programme in broilers to keep Salmonella levels under control, he said.