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 determin ed in sera from 306 dairy cows from 164 randomly selected herds in sou thern Ontario, Canada. Prevalences (and 95% confidence intervals) of a ntibodies capable of neutralising VTs from the following reference str ains of E. coli were: Strain H30 (VT1), 78.4% (73.7%-83.1%); Strain 32 511 (VT2, VT2v), 1.3% (0-2.9%); Strain 933W (VT2), 5.6% (3.0%-8.2%); S train K12B (VTe), 12.1% (8.5%-15.7%). Thirty-nine sera contained neutr alising antibodies to more than one type of VT. Thus, neutralising ant ibodies to verocytotoxins were common among dairy cows in Ontario, Can ada. At the individual-cow level, increased risk of VT1 antibodies was observed in association with an increase in age and in Holstein-Fries ian 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 t o handle both manure and feed.