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Title: ESCHERICHIA COLI O157:H7 IN A COHORT OF WEANED, PRECONDITIONED RANGE BEEF CALVES

Author
item DUNN, JOHN
item Keen, James
item DEL VECCHIO, RON
item WITTUM, THOMAS
item THOMPSON, R

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2004
Publication Date: 11/1/2004
Citation: Dunn, J.R., Keen, J.E., Del Vecchio, R., Wittum, T.E., Thompson, R.A. 2004. Escherichia coli O157:H7 in a cohort of weaned, preconditioned range beef calves. Journal of Food Protection. 67(11)2391-2396.

Interpretive Summary: Escherichia coli O157 is an important cause of foodborne disease. Cattle are known reservoirs of this bacteria and have been implicated in transmission to humans, usually via meat. Prevalence data for E. coli O157 in pre-feedlot beef calves is limited. Using sensitive E. coli O157 detection methods, a group of 408 weaned beef calves derived from 29 Southern cow-calf herds was sampled before (at fall weaning) and after a 45-day preconditioning period in order to estimate fecal E. coli O157 prevalence and to describe changes in fecal shedding during pre-conditioning. Calves were placed on a transition feed ration containing oxytetracycline (200 grams/ton) for forty-five days. Initial animal-level fecal point E. coli O157 prevalence was 2.5% (10/408) and included cattle originating from 5 of the 29 herds (17.2% herd-level prevalence). Fecal shedding of E. coli O157 was not detected in any cattle at the end of preconditioning. The absence of fecal shedding following the forty-five-day feeding period might be attributable to seasonal influences, inhibitory concentrations of oxytetracycline in the transition ration, or transient colonization. These findings suggest that E. coli O157 is widely dispersed at low prevalence in southern U.S. pre-feedlot weaned calves. Preconditioning programs might be useful for incorporating pre-harvest intervention strategies targeting control or prevention of E. coli O157 in feedlot cattle.

Technical Abstract: Escherichia coli O157:H7 (EC O157) is an important cause of foodborne disease. Cattle are reservoirs for the bacteria and implicated in transmission to humans. Prevalence data in pre-feedlot calves are limited. Using sensitive methods, a cohort of weaned beef calves (n=408) was sampled before and after preconditioning to estimate fecal point prevalence and describe changes in EC O157 fecal shedding. EC O157 isolates were confirmed and characterized by polymerase chain reaction and pulsed-field gel electrophoresis (PFGE). Calves from twenty-nine cow-calf farms were commingled at three preconditioning sites and placed on a transition ration containing oxytetracycline (200 grams/ton) for forty-five days. Initial animal-level fecal point prevalence was 2.5% (95% CI: 1, 5) with a herd-level prevalence of 17.2% (95% CI: 6, 36). Point prevalence following the preconditioning feeding period was 0%. An unexpected finding in our study was EC O157 isolates that were shiga-toxin deficient. PFGE subtypes of EC O157 were unique in epidemiologically unlinked herds, except one herd that had two unique subtypes. We expected, but observed neither increased fecal shedding in the cohort nor horizontal transmission of unique EC O157 subtypes. The absence of fecal shedding following the forty-five-day feeding period might be attributable to seasonal influences, inhibitory concentrations of oxytetracycline in the transition ration, or transient colonization that ended prior to sampling. EC O157 is apparently widely dispersed at low prevalence in U.S. pre-feedlot weaned calves.