Effect of supplementing corn‐ or barley‐based feedlot diets with canola oil on faecal shedding of Escherichia coli O157:H7 by steers

Aims: This study was conducted to evaluate the effect of supplementing barley‐ or corn‐based diets with canola oil on faecal shedding of Escherichia coli O157:H7 by experimentally inoculated feedlot cattle. Methods and Results: Four groups of yearling steers fed on barley‐ or corn‐based feedlot diets containing 0% (BA; CO) or 6% canola oil (BA‐O; CO‐O) were inoculated with 1010 CFU of a mixture of four nalidixic acid‐resistant strains of E. coli O157:H7. The inoculated strains were tracked in oral (mouth swab) and environmental (water, water bowl interface, feed, faecal pat) samples by enrichment and immunomagnetic separation (IMS) for 12 weeks, and in rectally collected faecal samples for 23 weeks (enumeration by dilution plating for 12 weeks; detection by IMS for a further 11 weeks). Levels of E. coli O157:H7 shed in faecal samples over the course of the enumeration period were similar (P = 0·14) among treatments. Disappearance of the inoculated strains from faeces was more rapid (P = 0·009) with barley than with corn, but shedding levels at the end of the enumeration period were similar (P = 0·21) across grain types. Canola oil supplementation did not affect (P = 0·71) the rate of disappearance of E. coli O157:H7 from faeces. The numbers of steers culture positive for E. coli O157:H7 during the enumeration period were similar (P = 0·57) among treatments. During the 11‐week detection period, however, more (P