# Investigating farm-level risk factors for Salmonella Dublin infection and on-farm transmission in British Columbian dairy farms

## TL;DR

A study of 70 BC dairy farms found that housing multiple cows in maternity pens increases Salmonella Dublin risk, but a Danish risk tool failed to reliably identify infected herds.

## Contribution

The study evaluates the effectiveness of a Danish risk scoring tool for Salmonella Dublin in BC dairy farms and identifies a specific housing risk factor.

## Key findings

- Farms housing >1 adult cow in the maternity pen were 4 times more likely to be Salmonella Dublin positive.
- The Danish risk scoring tool failed to differentiate between Salmonella Dublin-positive and -negative herds in BC.
- Alternative measures like individual cow serology or clinical illness may better evaluate risk factors.

## Abstract

Summary: Seventy British Columbia (BC) dairy farms were surveyed about Salmonella Dublin risk factors from a Danish risk scoring tool. Farms were classified as possible for negative based on bulk tank milk (BTM) serology status from the province's surveillance program. Farms that often kept >1 adult in the maternity pen at a time were 4 times more likely to be Salmonella Dublin positive. However, overall, the tool failed to differentiate Salmonella Dublin-positive versus Salmonella Dublin-negative herds, which calls into question its utility in the BC dairy context.

Summary: Seventy British Columbia (BC) dairy farms were surveyed about Salmonella Dublin risk factors from a Danish risk scoring tool. Farms were classified as possible for negative based on bulk tank milk (BTM) serology status from the province's surveillance program. Farms that often kept >1 adult in the maternity pen at a time were 4 times more likely to be Salmonella Dublin positive. However, overall, the tool failed to differentiate Salmonella Dublin-positive versus Salmonella Dublin-negative herds, which calls into question its utility in the BC dairy context.

•Farms that housed >1 adult dairy cow in the maternity pen were 4 times more likely to be positive for Salmonella Dublin on BTM.•The Danish risk scoring tool failed to differentiate Salmonella Dublin-positive versus Salmonella Dublin negative herds in BC.•Alternative outcome measures may be more effective when evaluating risk factors, such as changes in BTM status, individual cow serology, or clinical illness.

Farms that housed >1 adult dairy cow in the maternity pen were 4 times more likely to be positive for Salmonella Dublin on BTM.

The Danish risk scoring tool failed to differentiate Salmonella Dublin-positive versus Salmonella Dublin negative herds in BC.

Alternative outcome measures may be more effective when evaluating risk factors, such as changes in BTM status, individual cow serology, or clinical illness.

A recent study found that 30% of all dairy farms in British Columbia (BC) were positive for Salmonella Dublin, which has prompted a need to determine how to properly manage and mitigate Salmonella Dublin within the province. The overarching goal of this study is to use the components of a Danish Salmonella Dublin risk scoring tool to perform a cross-sectional, exploratory study to evaluate whether the tool, or components therein, can differentiate between Salmonella Dublin bulk tank milk (BTM)-positive versus BTM-negative BC dairy farms. A total of 70 BC dairy producers completed the survey and were classified as positive or negative based of BTM surveillance results. Overall, the components outlined in the modified Danish tool failed to differentiate herds that were positive or negative for Salmonella Dublin on BTM, with only 2 risk factors being identified. Farms that reported housing more than one adult dairy cow in the maternity pen were 4 times more likely to be positive for Salmonella Dublin on BTM than farms that only kept one adult in the maternity pen at a time. Future research should seek to determine if further modifications to the risk factor survey would be useful, especially the inclusion of questions on factors that target introduction of Salmonella Dublin versus on-farm transmission of Salmonella Dublin.