A two-year surveillance study published in Frontiers shows that Salmonella vaccination programs are working in broiler breeder flocks, while unexpectedly revealing potential transmission pathways for the poultry pathogen.
The research revealed that three of the serotypes commonly vaccinated against — Typhimurium, Enteritidis and Infantis — accounted for less than 10% of Salmonella found in broiler breeders. These same serotypes represented approximately 45% of positive findings in Georgia processing plants as reported by the U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS).
"This is one of the first studies outside of vaccine trials to show this broad positive effect of vaccination for Salmonella serotypes at the broiler breeder level," Nikki Shariat, Ph.D., associate professor in the Department of Population Health, Poultry Diagnostic Research Center, University of Georgia College of Veterinary Medicine said.
The findings suggest that industry efforts over the past two decades — including routine monitoring, vaccination, and enhanced biosecurity — have successfully reduced target Salmonella populations in breeder flocks.
Questions emerge about infection sources
The study also raised important questions about alternative infection sources in poultry.
Using deep serotyping technology called CRISPR-SeroSeq, which can detect multiple serotypes in a single sample, the researchers discovered some unexpected serotype associations.
Notably, Salmonella serotypes Cerro and Mbandaka — typically found in cattle — showed strong positive associations, suggesting potential feed contamination as a transmission route, Shariat said.
Interestingly, these cattle-associated serotypes do not appear in Georgia FSIS data from broilers, suggesting they don't survive through grow-out and processing.
The study, which analyzed 568 environmental samples from broiler breeder flocks between 2020 and 2022, also found that 18% contained multiple serovars.
“This is significantly lower than in broiler flocks where over 50% of samples can contain multiple serotypes and is explained by industry efforts to reduce Salmonella in broiler-breeders,” Shariat explained.
Serotype Kentucky showed negative associations with other serotypes, often excluding them. This isn’t entirely surprising, Shariat said, since Kentucky is one of the most common serotypes found in poultry.
It may also indicate reduced competition from vaccine-suppressed serotypes. In other words, the findings suggest that since Salmonella vaccines are effective against Typhimurium, Enteritidis and Infantis, Kentucky’s population fills the niche. That also likely explains why serotypes Cerro and Mbandaka are also found in broiler-breeders.
Industry monitoring timelines may need reevaluation
The research also suggests industry monitoring timelines for Salmonella in broiler breeders may need reevaluation.
Salmonella prevalence peaked at in birds between 28-35 weeks of age — corresponding to peak egg production — yet standard sampling usually occurs at 16-17 weeks and 42 weeks, potentially missing peak shedding periods.
With approximately 35% of breeder samples testing positive for Salmonella, the research highlights the complexity of Salmonella transmission in integrated production systems.
"The next question is, how are broiler flocks becoming colonized with Salmonella if we don’t find matching serotypes in broiler breeders?" Shariat said. "What are the other reservoirs or transmission pathways?"
