Bacteria associated with clinical mastitis in dairy heifers

A 1-yr field investigation of clinical mastitis in heifers was carried out in 24 veterinary districts in Norway. Quarter lacteal secretions from cases that occurred prepartum or within 14 d postpartum were examined bacteriolo gically. The study included 1040 heifers with clinical mastitis, and the to tal number of quarters that were clinically affected was 1361. The organism s that were most frequently isolated from samples from these quarters were Staphylococcus aureus (44.3%), Streptococcus dysgalactiae (18.2%), Staph. a ureus together with Strep. dysgalactiae (1.2%), coagulase-negative staphylo cocci (12.8%), Arcanobacterium pyogenes (3.5%), A. pyogenes together with S trep. dysgalactiae (0.5%) or Staph. aureus (0.4%), and Escherichia coli (6. 4%). Of the coagulase-negative staphylococci, Staphylococcus simulans (53.7 %), Staphylococcus hyicus (14.8%), and Staphylococcus chromogenes (14.8%) w ere the most prevalent species. Except for a higher relative percentage of A. pyogenes in cases that occurred before parturition (8.2%) than in cases that occurred after parturition (2.7%), no significant differences were obs erved in the distribution of the various organisms among prepartum and post partum cases. Regional variations were observed in the distribution of orga nisms. The proportions of Staph. aureus and A. pyogenes were highest, and t he proportion of coagulase-negative staphylococci was lowest, in late autum n and early winter. The proportion of E. coli was highest in summer. In hei fers in which mastitis was associated with increased rectal temperature or other systemic signs, the proportion of clinically affected quarters that w ere infected with Staph. aureus was larger than that in heifers without sys temic reaction.