Risk Factors for Intramammary Infections on Bavarian Dairy Farms-A Herd-Level Analysis

This cross-sectional study aimed to (a) determine the apparent prevalence of mastitis pathogens and (b) to identify risk factors for intramammary infections (IMIs) at the herd level in dairy herds in Bavaria, Germany. A stratified random sample of 305 herds was selected based on herd size, administrative district, and season. During the farm visits between July 2023 and July 2024, management data were recorded, quarter milk samples (QMSs) from 14,700 lactating cows were collected aseptically and analyzed, and the somatic cell count (SCC) at the quarter level was determined. Risk factors for the within-herd prevalence of Staphylococcus (S.) aureus, Streptococcus (Strep.) uberis, Strep. dysgalactiae, and non-aureus staphylococci (NAS) were analyzed by negative binomial regression, while risk factors for the presence of Escherichia (E.) coli and Strep. agalactiae IMIs on dairy farms were identified by logistic regression. The most frequently detected pathogens were NAS, found in 5.0% of all QMSs (n = 57,251), followed by Strep. uberis (1.9%) and S. aureus (1.8%), Strep. agalactiae (0.2%), and E. coli (0.1%). At the herd level, NAS, Strep. uberis, S. aureus, and Strep. dysgalactiae were found in 92%, 69%, 67%, and 57% of farms, respectively. Risk factors for increased within-herd prevalence included automated milking systems (NAS), organic production (Strep. uberis, S. aureus), straw bedding (Strep. uberis), and lack of bedding or mattress cubicles (Strep. dysgalactiae). The odds for a herd to be positive were increased with audible liner slips (E. coli) and the irregular cleaning of water troughs (Strep. agalactiae), and without a maintenance agreement for milking equipment (Strep. agalactiae). These results provide valuable insights into options for the targeted prevention of IMI.