Year-Long Prevalence and Antibiotic Resistance Profiles of Salmonella enterica Serogroups Isolated from a Wisconsin Dairy Farm

<i>Salmonella enterica</i> infections can significantly impact the health and productivity of dairy cattle. Asymptomatic carriage of <i>Salmonella</i> can make it difficult to identify and monitor this pathogen across a herd. Therefore, a more focused <i>Salmonella</i> census on dairy farms is needed to better understand the dynamics of asymptomatic carriage. Here, we monitored the prevalence of <i>Salmonella enterica</i> on a dairy operation in Wisconsin, USA. Fecal samples were collected over 12 months from cattle and the farm environment, subjected to <i>Salmonella</i> isolation, serogrouped, and tested for antibiotic resistance. <i>Salmonella</i> was highly prevalent on this farm, with an average of 90% of the cattle being carriers. Total recovery of <i>Salmonella</i> from environmental samples ranged from 40 to 90%. Four serogroups were identified on the farm, with K being most common in cattle and C being most common in the environment. Antibiotic resistance was tested against eight antibiotics and was found to be highest for neomycin (44.5%) and sulfadimethoxine (86.3%). Our data show that serogroups associated with asymptomatic carriages are persistent and highly prevalent, with niche specificity to different locations. These results provide useful information for studying within-herd transmission of <i>Salmonella</i> and contributes to our understanding of transmission risks within the farm ecosystem.