DAIRY MANAGEMENT PRACTICES AND THE TRANSMISSION OF ZOONOTIC PATHOGENS IN MILK
Title: Factors associated with Salmonella presence in environmental samples and bulk-tank milk from U.S. dairies
Submitted to: Zoonoses and Public Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 2010
Publication Date: May 31, 2010
Citation: Ruzante, J., Lombard, J., Wagner, B., Fossler, C., Karns, J.S., Van Kessel, J.S., Gardner, I. 2010. Factors associated with Salmonella presence in environmental samples and bulk-tank milk from U.S. dairies. Zoonoses and Public Health. Available: http://dx.doi.org/10.1111/j.1863-2378.2010.01333.x
Interpretive Summary: Bacteria of the genus Salmonella cause gastrointestinal disease in humans. Dairy farms are known reservoirs of Salmonella and human outbreaks of salmonellosis are sometimes associated with dairy products. This study describes the analysis of data on the presence of Salmonella bacteria on U.S. dairy farms and in the raw bulk tank milk produced on those farms obtained during a nationwide survey. Environmental samples, bulk tank milk, and inline milk filters were analyzed for the presence of Salmonella and statistical analyses were used to determine factors associated with the detection of Salmonella in bulk tank milk. The data showed that factors such as the region of the country and herd size were associated with the occurrence of Salmonella in bulk tank milk. Several dairy management practices were also correlated with increased risk of Salmonella contamination of bulk tank milk. This study will aid farmers, dairy processors, and scientists in efforts to reduce the incidence of Salmonella on dairy farms and to reduce or eliminate Salmonella from bulk tank milk.
The objective of this study was to evaluate herd characteristics and management practices associated with presence of Salmonella in the farm environment and in bulk tank milk (BTM) in U.S. dairy herds. Herd management data, environmental culture, bulk tank milk and in-line milk filter polymerase chain reaction results for Salmonella from 260 U.S. dairy herds surveyed during the National Animal Health Monitoring System Dairy 2007 study were analyzed. Herd characteristics and management practices were screened by univariate analysis, and selected variables were used to construct a logistic regression model to identify factors associated with the presence of Salmonella in environmental samples. To identify factors associated with the occurrence of Salmonella in bulk tank milk and milk filters, a priori selected variables that were related to milking procedures were analyzed univariately and a logistic regression model was constructed. The presence of Salmonella in the farm environment was associated with location of the operation in the East (OR = 4.8; CI: 1.9-11.6), not using a broadcast manure spreader (OR = 3.2; CI: 1.4-7.5), use of bovine somatotropin (BST) (OR = 2.7; CI: 1.5-5.0) and use of anionic salts (OR = 2.2; CI: 1.2-3.9). In the final multivariable model, herds with fewer than 100 cows were at decreased odds (OR = 0.3; CI: 0.1-0.7) of being culture positive for Salmonella as were herds with between 100 and 499 cows (OR = 0.4; CI: 0.2-0.8) compared with herds having 500 or more cows. The presence of culture-positive environmental sample and herd size were significantly associated with Salmonella BTM contamination. The herd-level factors identified in this study were in agreement with prior studies but also identified other potential factors that can be targeted in Salmonella control programs.