The carriage of E. coli O157H:7 by slaughter cattle into packing plants is an important beef safety issue. Cattle producers, packing plant officials, scientists, journalists, association personnel and government officials have argued that farmers/ranchers need to assume responsibility to prevent (or at least minimize) the risk that slaughter cattle would carry food borne pathogens, on or in their bodies, into packing plants.
Numerous studies have shown the prevalence of E. coli O157:H7 to range from 23-100%. These studies monitored farms and ranches, breeding herds, feedlots, etc. Mirtsching (2002) said “Based on three years of data, testing hides of incoming cattle: (a) If 15 to 20% of cattle in a pen are contaminated with E. coli O157:H7, our interventions (multiple hurdle carcass decontamination system) prevent occurrence on carcasses. (b) If 40% or more of cattle are contaminated with E. coli O157:H7, our interventions will not prevent occurrence on carcasses.”
Robert Elder (ARS-USDA) reported at the E. coli Summit in 2003 that 7.4% of all calves tested were fecally shedding E. coli O157:H7 (Smith et al., 2003). Producer Group Conclusions: Preharvest Intervention (National Cattlemen’s Beef Association, 2003) included statements that 25% of calves shed E. coli O157:H7 within a week of birth, 87% of calves are exposed to E. coli O157:H7 prior to weaning, infection/reinfection at the feedlot is ongoing, and studies that are incomplete include those involving direct-fed microbials, vaccines, sodium chlorate, probiotics, and competitive inhibition/exclusion procedures. Jim Keen (ARS-USDA) said, at the E. coli Summit in 2003, that 50% of ranches and 100% of feedlots have E. coli O157:H7; which indicates the pathogen is endemic in the U.S. (Smith et al., 2003). Lahti et al. (2003) in a Finnish cattle finishing study, reported that calves sampled in trucks were negative for E. coli O157:H7 on arrival at the finishing farm but positive animals were detected one day later. If the U.S. beef industry expects to break the infection chain, a logical point at which to direct risk mitigation efforts is as calves are weaned.
The objectives of this study were as follows:
One hundred forty-three (143) gestating beef cows in the last trimester of pregnancy were used for this experiment. Cows were previously synchronized and artificially inseminated and were expected to calve within a thirty day period. Approximately one-half (n=74) of the cows were vaccinated with an experimental vaccine designed to prevent the attachment of E. coli O157 to the intestinal wall, and then co-mingled with the remaining (n=69) non-vaccinated control cows.
Fecal samples were collected from the cows (n=143) and calves (n=143) and analyzed for the prevalence of E. coli O157:H7. The swab fecal sample was collected from every cow on d-0 (before vaccination) and 9-14 days after parturition. The calves were also swabbed for a fecal sample on the post calving date and again at ~60 days after birth (branding). Fecal samples were evaluated for prevalence of E. coli O157 following enrichment, use of immunomagnetic separation, and plating on ctSMAC and Rainbow agars. Morphologically typical colonies were tested for latex agglutination. Samples positive for latex agglutination were subjected to most probable number analysis.
The results from the fecal analysis indicated that none of the cows tested positive for E. coli O157:H7. The first sampling on the calves was negative as well. Only on the last sample of the calves was there a positive sample. Three of the 69, or 4.3%, control calves tested positive for E. coli, with one of those calves being a super shedder (1100 MPN/g). Five of the 74, or 6.6%, vaccinated calves tested positive for E. coli. However, the five all had numbers ≤3 MPN/g. No significant differences (P >0.05 in prevalence were found between control calves and the vaccinated calves.
Due to limited number of animals found positive for fecal samples in this study, additional research is needed to establish the potential effectiveness of vaccines against E. coli O157:H7 in pre-harvest interventions.