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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:
A total of 756 cattle (389 heifers and 367 steers) were selected from a single herd in central MT for use in this study. The selected herd was composed of Angus and Simmental genetics and primarily calves in February and March. The calves selected were randomly removed from their mothers (weaned) over a three-week period in October of 2003 with approximately one third of the calves being weaned per week. On the day of weaning, calves were transported from pasture to a receiving yard consisting of six, 150 hd pens and an appropriate cattle handling facility. Upon arrival at the receiving yard, calves were sorted by gender (steers vs. heifers), placed in holding pens and then processed separately. As calves entered the processing chute half (every other animal) were given an experimental Escherichia coli vaccination (E-vac) designed to prevent the attachment of Escherichia coli O157:H7 to the intestinal wall of cattle. A second dose (booster) was given on d 21. Following processing, calves were allotted to pens as they exited the chute; resulting in pens with a final disposition of approximately 50% E-vac and 50% control within gender.
At processing (d 0) 5 E-vac and 5 control calves from each pen were randomly selected for blood antibody titer analysis. Fecal samples were collected from all calves on d 0 and 45. All samples were analyzed for the presence of E. coli O157:H7.
Individual animal performance was monitored in order to detect any decreased performance that may be caused by the experimental vaccine. There were no statistically significant differences (P>0.10) in initial weight, final weight or average daily gain between vaccinated cattle and controls, indicating no change in performance due to the vaccine. While there were differences due to gender (steers had heavier initial and final weights compared with heifers), no differences in average daily gain were measured.
Irrespective of treatment, 9.4% of the animals were shedding E. coli O157:H7 at time of weaning and 3.9% were positive following the 45-d pre-conditioning period. Despite randomization, the initial prevalence in control calves was lower than the initial prevalence in calves which were to be vaccinated (6.8% vs. 12.0%). Following the 45-d pre-conditioning period, the prevalence of the pathogen in vaccinated calves was lower than in the control calves (2.7% vs. 5.1%). Initially, heifers had a higher prevalence than steers.
Results were limited due to low initial E. coli O157:H7 prevalence in feces samples, and low prevalence following vaccination. Additional studies are warranted to determine the potential effectiveness of using the experimental vaccine as an intervention technique for control of pre-harvest E. coli O157:H7 during the pre-conditioning phase of beef cattle production.