This study was designed to determine the prevalence of Escherichia coli O157:H7 infection of
beef calves at weaning, prior to arrival at the feedlot or mixing with cattle from other sources.
Fifteen range cow-calf herds, which weaned calves in October and November, were sampled in
Kansas, Missouri, Montana, Nebraska and South Dakota. Faecal culture for E. coli O157:H7
was performed and anti-O157 serum antibody titres were determined by blocking ELISA.
Thirteen of the 15 herds (87%) were found to have at least one positive isolation of E. coli
O157:H7 in faecal samples. Within positive herds, prevalence ranged from 1·7–20·0%, with an
average of 7·4±6·2% s.d. of individual animals shedding E. coli O157:H7 in faeces. All herds
had high prevalence of anti-O157 antibodies, ranging 63–100% of individuals within herds
seropositive. This study indicates that E. coli O157:H7 infection before weaning, prior to entry
into feedlots, is widespread. Furthermore, serologic evidence suggests that most calves (83%)
and all herds (100%) have been exposed to E. coli O157.