THE SEROPREVALENCE OF VEROCYTOTOXIN-PRODUCING ESCHERICHIA-COLI IN ONTARIO DAIRY-COWS AND ASSOCIATIONS WITH PRODUCTION AND MANAGEMENT

The prevalences of neutralising antibodies to verocytotoxins (VT) from four reference strains of VT-producing Escherichia coli were determined in sera from 306 dairy cows from 164 randomly selected herds in southern Ontario, Canada. Prevalences (and 95% confidence intervals) of antibodies capable of neutralising VTs from the following reference strains of E. coli were: Strain H30 (VT1), 78.4% (73.7%-83.1%); Strain 32511 (VT2, VT2v), 1.3% (0-2.9%); Strain 933W (VT2), 5.6% (3.0%-8.2%); Strain K12B (VTe), 12.1% (8.5%-15.7%). Thirty-nine sera contained neutralising antibodies to more than one type of VT. Thus, neutralising antibodies to verocytotoxins were common among dairy cows in Ontario, Canada. At the individual-cow level, increased risk of VT1 antibodies was observed in association with an increase in age and in Holstein-Friesian cows compared with other breeds. The herd-level proportion of VT1-positive cows was reduced in association with an increase in herd size, storage of manure in an open pile, and occasional use of equipment to handle both manure and feed.