Navigating complexity: Salmonella Dublin risks factors in a Midwestern US calf movement system.

Movement of live cattle is a known risk for pathogen spread. Understanding movement patterns, particularly at high-risk commingling facilities, is essential for targeted pathogen surveillance and disease mitigation strategies. This repeated cross-sectional study investigated calf movement patterns and detection of Salmonella spp. (including Salmonella Dublin) within a Midwestern livestock dealer facility, a critical yet underexplored component of the US cattle supply chain. From May to October 2023, records of 1,184 calf movements were analyzed alongside identification of Salmonella spp. by culture and Salmonella Dublin via PCR from environmental sampling. Weekly network metrics were assessed, including number of incoming sources, density, and source stability (Jaccard similarity indexes [JSI]). Mixed-effects logistic regression models were used to evaluate the association between movement patterns and pen-level pathogen detection. Results revealed a high number of sources and animals passing through the facility, with fluctuating connectivity over time. Environmental sampling confirmed variable Salmonella Dublin presence, with a significant decreasing trend over time, despite peak Salmonella spp. detection in late summer. Weekly movement networks showed variability in source stability, with lower JSI values (i.e., more variation in source ZIP codes) typically preceding increased detection of Salmonella Dublin, suggesting that introduction of new or shifting sources may be a risk factor. These results highlighted the need for further research into which characteristics of these new sources, such as geography, management practices, or biosecurity, might contribute to Salmonella Dublin presence and potential persistence. Findings from this study underscored the role of livestock dealer networks in pathogen occurrence and reinforced the need for targeted mitigation strategies at such facilities. Strengthening external biosecurity through accurate and accessible intra- and interstate movement records and environmental monitoring is vital for mitigating the risks of Salmonella Dublin, a pathogen of critical concern for public and animal health.