A Prevalence Survey of Salmonella in Raw Milk in Ontario, 1986-87

In a survey to determine the incidence and prevalence of Salmonella in the bulk milk supply of dairy farms in southwestern Ontario 1986-87, milk filters from 813 farms were cultured over four sampling periods in six months. Prevalence rates during the four sampling periods were as follows: September 1986: 1.23%; October-November: 0.40%; December-January: 0.19%; and February 1987: 0%. Incidence rates increased from 0.15% per month in the first sampling period to 0.20% in the second and third period, then dropped to 0% in the fourth sampling period. Eight isolates of S. muenster and two of S. mbandaka were recovered from nine different farms. All of the isolates were sensitive to the commonly used antimicrobials tested. Owing to the steady decline in the prevalence over the study period, no seasonal patterns were apparent. The results of this survey indicate that the presence of Salmonella in bulk milk supplies is dynamic.