Does It Have To Be F5 Positive to be Significant?

F5 positive isolates can certainly be the cause of scours in calves, however, F5 positive isolates are less commonly isolated in cases submitted to our laboratory for neonatal scours, likely because the F5 pilus is included as an antigen in commercial E. coli bacterins so prevalence is reduced through the use of a standard pre-calving vaccination regime. F5 negative isolates may still be ETEC strains and have toxin genes. These strains may not be included in commercially available products and have been shown to cause neonatal scours.