Pen-level prevalence of Salmonella enterica spp. enterica in faecal samples collected from beef-on-dairy cattle

Abstract

Salmonella enterica is a foodborne pathogen of major public health concern. In the US, non-typhoidal Salmonella is estimated to cause annually about 1.35 million infections, 26,500 hospitalizations, and 420 deaths. Salmonella enterica is a significant food safety concern in cattle and contamination of beef occurs mainly through faecal contamination and by Salmonella infected lymph nodes. The use of beef cattle semen to breed dairy cows to produce calves, called, beef-on-dairy (BOD) cattle, for beef production has greatly increased in the past 5 years. There are no studies in the United States on the prevalence of Salmonella enterica and its public health implications to food safety in BOD grower cattle. Our objectives were to conduct a comprehensive analysis of feeding and management practices, including data on morbidity and mortality, from birth to harvest to determine their associations with the Salmonella enterica prevalence in faeces. A total of 148 pen floor faecal samples were collected randomly from grower yards in Kansas (n=40), Nebraska (n=40), and Texas (n=68). These samples were not pooled and were processed individually. Because the samples were collected from the pen floor, the identity and number of individual animals represented in each sample remained unknown, and results were interpreted at the pen level. Salmonella enterica isolation and identification were done by culture method, agglutination and PCR detection of species-specific invA and pagC genes. Overall prevalence of Salmonella enterica with PCR was 18.2% (27/148). The prevalence was 7.5% (3/40), and 35.3% (24/68) in Kansas and Texas, respectively. All the samples from Nebraska were negative for Salmonella. Efforts are ongoing to collect more faecal samples from different phases of the life cycle in major cattle producing states in the US, along with the data on feeding and management practices. Further studies are directed towards molecular characterization of Salmonella isolates to better understand the ecology and its public health implications.