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.