449 454 Wageningen Academic Publishers Wageningen, Netherlands

When designing both regional and herd-specific mastitis control and research programs, recent knowledge about the distribution of clinical and subclinical pathogens, as well as the frequency of adoption of mastitis prevention practices have to be considered. The objectives of this study were to estimate the prevalence of the three most important contagious pathogens on Prince Edward and to study the association between the prevalence of different mastitis pathogens and the bulk milk somatic cell count (BMSCC). Fresh bulk tank milk was obtained of all 258 PEI dairy herds. Bulk tank samples were obtained three times, with a weekly interval. BMSCC and the presence of Staphylococcus aureus, Streptococcus agalactiae and Mycoplasma spp. was evaluated using culture media that are specific for each pathogen. The cumulative prevalence for Staph. aureus, Strep. agalactiae and Mycoplasma spp. was 74, 1.6 and 1.9%, respectively. Staphylococcus aureus-positive herds had a geometric mean BMSCC of 169 000, cells/ml compared to 129 000 cells/ml in herds with no contagious pathogens. The 4 Streptococcus agalactiae-positive herds and the 5 Mycoplasma spp. positive herds had a geometric mean BMSCC of 177 000 cell/ml and 137 000 cells/ml, respectively. The frequency of which Staphylococcus aureus was isolated was positively correlated to the average BMSCC. Prevalence of Streptococcus agalactiae was much lower than expected and Mycoplasma spp. in bulk milk was reported for the first time on Prince Edward Island and in Canada for the first time since 1972.