Description:
<jats:p>A total of 2538 quarter milk samples from 638 lactating dairy cows from 47 farms in the canton of Bern, Switzerland, were investigated for streptococci. A novel, simple and inexpensive laboratory method was used for the differentiation of <jats:italic>Streptococcus</jats:italic> species, and a risk factor analysis was carried out. The prevalence in the quarter milk samples was 0.2 per cent for <jats:italic>Streptococcus agalactiae</jats:italic>, 1.3 per cent for <jats:italic>Streptococcus uberis</jats:italic>, 1.3 per cent for <jats:italic>Streptococcus dysgalactiae</jats:italic>, 0.1 per cent for <jats:italic>Enterococcus</jats:italic> species and 2.9 per cent for minor <jats:italic>Streptococcus</jats:italic> species (designated <jats:italic>Streptococcus‐Lactococcus‐Enterococcus</jats:italic> [SLE] group). Based on the somatic cell count (SCC), <jats:italic>S uberis</jats:italic> and <jats:italic>S dysgalactiae</jats:italic> were classified as ‘major’ pathogens and the bacteria in the SLE group as ‘minor’ pathogens. For <jats:italic>S uberis</jats:italic>, <jats:italic>S dysgalactiae</jats:italic> and bacteria in the SLE group, the most significant risk factor was an intramammary infection (IMI) of a neighbouring quarter by the same pathogen. Other significant risk factors for <jats:italic>S uberis</jats:italic> infection were a positive California Mastitis Test (CMT) result and a SCC of more than100,000 cells/ml. Significant risk factors for IMI with <jats:italic>S dysgalactiae</jats:italic> were a positive CMT result, teat injury and palpable abnormalities in the udder. Infection with bacteria in the SLE group was significantly associated with a SCC of more than 100,000 cells/ml, a lactation number of more than 2, the right rear quarter (as the location of infection) and a positive CMT result.</jats:p>