Are Severe Mastitis Cases in Dairy Cows Associated with Bacteremia?

SIMPLE SUMMARY: The occurrence of bacteremia associated with cases of severe mastitis in dairy cows is an under-researched topic and of great practical importance for the development of evidence-based strategies in mastitis therapy. The aim of this study was to determine the occurrence of bacteremia in lactating dairy cows with severe mastitis cases. For this purpose, we worked on the detection of culturable pathogens in the blood to obtain information on whether systemic antibiotic therapy is necessary in cases of severe mastitis. Detection of culturable pathogens in the blood of cows with severe clinical mastitis was apparently rare (1.4%). Further studies are necessary to estimate the occurrence of bacteremia in severe bovine mastitis. ABSTRACT: The objective of this study was to investigate the occurrence of bacteremia in dairy cows with severe mastitis. Milk samples were collected from affected udder quarters, and corresponding blood samples were collected from dairy cows with severe mastitis at the time of diagnosis before any therapeutic measures were undertaken. The cultural detection of pathogens in blood classified a bacteremia. Further diagnostic tests were performed to provide evidence of bacteremia. This was realized by PCR with regard to S. aureus, E. coli and S. uberis and the Limulus test. Detection of culturable pathogens in the blood of cows with severe clinical mastitis was rare and occurred in only one of 70 (1.4%) cases. Overall, bacterial growth was detected in 53 of 70 (75.7%) milk samples. S. uberis (22/70), E. coli (12/70) and S. aureus (4/70) were the most frequently isolated pathogens from milk of cows with severe mastitis. PCR was performed in 38 of 70 (54.3%) blood samples. PCR was positive in eight of 38 cases. S. uberis was found most frequently in six blood samples (8.6%). E. coli was found on PCR in one blood sample (1.4%). S. aureus was identified in one blood sample (1.4%). When Coliforms were detected in the quarter milk sample, a Limulus test was performed in the corresponding blood sample. In three of 15 cases, the Limulus test was positive (4.3% of samples). Further studies are needed to investigate the occurrence of bacteremia in cows with severe mastitis in a higher population size.