title: A randomized controlled trial to assess the impact of dietary energy sources, feed supplements, and the presence of super-shedders on the detection of Escherichia coli O157:H7 in feedlot cattle using different diagnostic procedures.
abstract: Alteration of the gastro-intestinal tract through manipulation of cattle diets has been proposed as a preharvest control measure to reduce fecal shedding of Escherichia coli O157:H7. The objective of this study was to examine the effects of the energy source's moisture content (high moisture corn and dry whole-shelled corn), two natural feed supplements (Saccaromyces cerevisiae boulardii CNCM 1079-Levucell and Aspergillus oryzae-Amaferm), and two levels of vitamin A (2200 IU/kg and no supplementation) on the fecal excretion of E. coli O157:H7 in naturally infected cattle. One hundred sixty-eight Angus-cross beef steers were randomly allocated to 24 pens, and each pen was assigned 1 of 12 dietary treatments in a randomized complete block design. E. coli O157:H7 was detected by rectoanal mucosal swab (RAMS) and fecal grab samples using immunomagnetic separation (IMS) and standard microbiological techniques. On the basis of multivariable multilevel logistic regression models, we found a statistically significant (p < 0.05) increase in the prevalence of E. coli O157:H7 in animals fed dry whole-shelled corn in models based on fecal-IMS, and this effect was increased if a super-shedding animal (shedding > 10(4) colony forming units of E. coli O157:H7 per gram of feces) was present in the pen at the time of testing relative to animals fed high moisture corn and nonexposed to super-shedders. However, in similar models based on RAMS-IMS testing, the effect of corn type on the prevalence of E. coli O157:H7 varied with the type of feed additive used. Being exposed to a super-shedding pen-mate also increased the odds of being positive to E. coli O157:H7 in the RAMS-IMS models. These models demonstrate that the impact of different supplements may vary with the diagnostic test used, and that further research into the biological significance of differences between RAMS- and fecal-IMS test results is warranted.
authors.affiliation: Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada. ncernicc@uoguelph.ca
authors.forename: Natalia
authors.initials: N
authors.lastname: Cernicchiaro
authors.forename: David L
authors.initials: DL
authors.lastname: Pearl
authors.forename: Scott A
authors.initials: SA
authors.lastname: McEwen
authors.forename: Henry N
authors.initials: HN
authors.lastname: Zerby
authors.forename: Francis L
authors.initials: FL
authors.lastname: Fluharty
authors.forename: Steve C
authors.initials: SC
authors.lastname: Loerch
authors.forename: Michael D
authors.initials: MD
authors.lastname: Kauffman
authors.forename: Jaime L
authors.initials: JL
authors.lastname: Bard
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: LeJeune
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000175:diagnosis* / Q000382:microbiology*; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D004224:Diterpenes; D002149:Energy Intake; D004927:Escherichia coli Infections / Q000175:diagnosis / Q000382:microbiology / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D008297:Male; D019936:Probiotics / Q000008:administration & dosage; D000084562:Retinyl Esters; D014801:Vitamin A / Q000008:administration & dosage / Q000031:analogs & derivatives; D003313:Zea mays
chemical_list: D004224:Diterpenes; D000084562:Retinyl Esters; D014801:Vitamin A; C009166:retinol acetate