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1 Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan 66506
2 Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506
* To whom correspondence should be addressed. E-mail: tnagaraj{at}vet.k-state.edu.
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Abstract |
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Hindgut is a major colonization site for E. coli O157 in cattle. In this study, diets were formulated to effect changes in hindgut fermentation to test our hypothesis that changes in hindgut ecosystem could have an impact on fecal shedding of E. coli O157. Feedlot heifers (n = 347) were pre-screened for prevalence of E. coli O157 by fecal and rectoanal mucosal swab (RAMS) cultures. A subset of 40 heifers identified as being positive for fecal shedding of E. coli O157 were selected, housed in individual pens, and randomly allocated to 4 dietary treatments. Treatments were arranged as a 2 x 2 factorial, with factor 1 consisting of grain type (sorghum or wheat) and factor 2 being method of grain processing (steam-flaking or dry-rolling). Four transition diets, each fed for 4 days, were used to adapt the animals to final diets that contained 93% concentrate and 7% roughage. The grain fraction consisted of dry-rolled sorghum, steam-flaked sorghum, a mixture of dry-rolled wheat and steam-flaked corn , or a mixture of steam-flaked wheat and steam-flaked corn. Wheat diets contained 52% wheat and 31% steam-flaked corn (DM basis). Fecal and RAMS samples were obtained 3 times a week to isolate (enrichment, immunomagenetic separation, and plating on selective medium) and identify (sorbitol negative, indole production, and agglutination test) E. coli O157. Data were analyzed as repeated measures of binomial response (positive or negative) on each sampling day. Method of processing (dry-rolled vs. steam-flaked), sampling day, and the grain type x day interaction were significant (P < 0.05), but not the method of processing x grain type interaction. Average prevalence of E. coli O157 from d 9 was greater (P < 0.001) in cattle fed steam-flaked grains (65%) compared to those fed dry-rolled grains (30%). Average prevalence in cattle fed sorghum (50%) or wheat (30%) were similar (P > 0.10) on most sampling days. Results from this study indicate that feeding dry-rolled grains compared to steam-flaked grains reduced fecal shedding of E. coli O157. Possibly, dry-rolling allowed more substrate to reach the hindgut where it was fermented, thus making the hindgut inhospitable to the survival of E. coli O157. Dietary intervention to influence hindgut fermentation offers a simple and practical mitigation strategy to reduce prevalence of E. coli O157 in feedlot cattle.
Key Words: E. coli O157, fecal shedding, finishing cattle, grain processing, preharvest intervention
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