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The Impact of Dietary Distillers' Grains on Escherichia Coli O157:H7 in Cattle, and Interventions to Reduce the Potential Food Safety Impact

Nagaraja, Tiruvoor G
Kansas State University
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  1. Determine whether the fecal shedding of E. coli O157:H7 is affected by the supplemental level and form (dry vs. wet) of distiller grains (DG) in the diet and whether subsequent removal of DG decreases fecal shedding.
  2. Compare the magnitude and prevalence of E. coli O157:H7 in feces and subsequent hide and carcass contamination of slaughtered cattle that did or did not receive DG in their feed during the pre-harvest phase.
  3. Evaluate the effectiveness of intervention strategies for reducing fecal shedding of E. coli O157:H7 in cattle receiving DG.
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NON-TECHNICAL SUMMARY: Escherichia coli O157:H7 causes food-borne gastroenteritis in thousands of Americans each year. Cattle are a major reservoir of the organism, which resides in the gastrointestinal tract, particularly the hindgut, and is shed in the feces. Cattle feces are a major source of contamination of beef products, produce, and recreational and drinking water. Factors contributing to the fecal shedding of E. coli O157:H7 in cattle and potential pre- and post-harvest intervention strategies to minimize human health risks are of primary concern for food safety. Despite rigorous surveillance of meat processors by the USDA Food Safety and Inspection Service, the number of confirmed human illnesses caused by E. coli O157:H7 continues at unacceptable levels. Distiller's grains (DG) are a co-product of ethanol production from cereal grains. The DG is a valuable livestock feed and offers cattle producers an opportunity to reduce feed costs without compromising animal health and performance. The availability and use of DG is projected to continue a dramatic increase with the expanded demand for ethanol fuel. Previously, fecal shedding of E. coli O157:H7 was shown to be positively associated with feeding DG in cattle. The proposed research would greatly enhance our understanding of the relationship between dietary DG and E. coli O157:H7 in cattle, including potential contamination of carcasses at slaughter, and provide an opportunity to evaluate existing and novel intervention strategies to mitigate potential risks associated with feeding this valuable co-product.

APPROACH: In the first objective, effects of amount and form (wet or dry) of DG in cattle finishing diets on fecal prevalence of E. coli O157:H7 will be determined. During the second phase of the study, DG will be removed from diets as further evidence for a causal relationship and as a possible pre-harvest intervention strategy. Cattle in a research feedlot will be randomly allocated to 84 pens with 15 cattle per pen. One of 7 treatments will be randomly assigned to each pen: wet DG or dried DG, and each supplemented at 10, 20, or 40% of the diet. A group with 0% DG will serve as the control. Each treatment will have 12 pens. After 4 months, the DG will be removed from 6 of 12 pens and cattle in those pens will be fed control diets. Fecal samples will be collected once every two weeks for the first 16 weeks. Then DG will be removed from 6 of 12 pens on DG treatments and fecal samples will be collected once per week for 3 weeks. Ten pen-floor fecal samples will be collected from each pen at each sampling time and cultured for E. coli O157:H7. Generalized linear mixed models with repeated measures will be used to evaluate potential differences in E. coli O157:H7 prevalence between treatment groups. In the second objective, prevalence estimates for fecal shedding, high-concentration shedding (based on semi-quantification), and hide and carcass contaminations between cattle fed DG and those not fed DG will be determined. Additionally, pulsed-field gel electrophoresis will be used to establish clonal connection between fecal, hide, and carcass isolates. Samples will be collected from truck loads of finished cattle at a commercial abattoir. Samples will be transported to the laboratory and cultured for E. coli O157:H7. A semi-quantitative method will be employed to categorize fecal culture positive cattle into low shedders (lower than 5 x 104 CFU/g) and high shedders (higher than 5 x 104 CFU/g). Diet composition fed during the finishing phase of sampled cattle will be obtained from the feedlots. Feedlot confidentiality will be maintained throughout the study. Outcomes assessed will include fecal prevalence, the prevalence of high-shedding animals, hide prevalence, pre-evisceration carcass prevalence and potential differences in prevalence based on DG or no DG in the diet with truck load as the experimental unit. In the third objective, three pre-harvest intervention strategies (a direct-fed microbial, a vaccine and a plant product) will be evaluated for their ability to reduce the prevalence of E. coli O157:H7 in feedlot cattle fed DG. Cattle will be randomly allocated to 32 pens of 50 animals each after adaptation to the final finishing diet. One of four treatments will be randomly assigned to each pen: control (no intervention), direct-fed microbial, vaccine, or a plant product (brown seaweed). Cattle will be fed an identical finishing diet containing 25% supplemental DG. Fecal samples will be collected once every 30 days to determine prevalence of E. coli O157:H7. Generalized linear mixed modeling of prevalence and the repeated pen-measures of fecal prevalence will be used to investigate time-dependent effects of the intervention.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Legislation and Regulations
Escherichia coli
Bacterial Pathogens
Natural Toxins
Viruses and Prions
Chemical Contaminants