Risk factors associated with bacteriological quality of bulk tank milk in the Netherlands

Bulk tank milk culture can be used to evaluate farm hygiene practices and the prevalence of mastitis pathogens. The objective of this study was to determine associations between some risk factors and concentrations of selected bacteria in bulk tank milk of Dutch dairy farms. A questionnaire was conducted in December 2010 on 904 Dutch dairy farms which have participated for at least one year in the GD Animal Health Service bulk tank milk culturing program. Bulk tank milk was tested for counts of Staphylococcus aureus, streptococci and streptococci-like organisms (SSLO), and coliform bacteria as well as the presence of Streptococcus agalactiae, Streptococcus uberis, and Klebsiella spp. Complete questionnaire data and bulk tank milk culture results were available from all 904 Dutch dairy farms. For each bacteria species a stepwise backward multivariate analysis was performed. Farms using an automated milking system had higher counts of SSLO, coliforms, and S. aureus in BTM than farms with tie-stall or conventional milking systems. Teat cleaning by an automated milking system appeared to be less effective than manual cleaning. Tie-stall barns had higher S. aureus counts in the bulk tank milk. Farms with deep-bedding stalls tended to have fewer S. uberis and more often a low count of SSLO and S. aureus when compared with those farms using rubber mats or mattresses as bedding material. Barn type, bedding type, milking system, and pasturing were all associated with one or more bacterial counts in bulk tank milk.