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Feeding high levels (≥40% dry matter) of distillers grains may increase the risk for cattle to carry enterohemorrhagic Escherichia coli (EHEC) O157. The mechanism for the increased risk is not known nor whether non-O157 EHEC are similarly affected. Our objective was to test whether the fibre content or other components of modified distillers grains plus solubles (MDGS) affects the probability for cattle to carry EHEC serogroups of public health importance. A 2 × 2 plus 1 factorial treatment arrangement within a randomized block design was utilized. Within each of four blocks, 25 feedlot pens (n = 8 steers/pen) were assigned randomly to (i) corn-based control diet; (ii) 20% dry matter (DM) MDGS; (iii) 40% DM MDGS; (iv) corn bran added to corn-based diet to match fibre of 20% MDGS or (v) 40% MDGS. Rectoanal mucosa swabs (RAMS) were collected on day (d)0, d35, d70 and d105; hide swabs were collected on the last feeding day. Samples were tested for EHEC by a molecular screening assay. The effects of fibre source and fibre level on EHEC carriage were tested using multilevel logistic regression (generalized linear mixed models; α = 0.05). EHEC O45 RAMS detection was associated with fibre level, source and sampling day. EHEC O103 RAMS detection increased by feeding 40% MDGS but not the corresponding corn bran diet. Hide contamination by EHEC O45 or O103 was less likely in cattle fed MDGS compared to corn bran diets. EHEC O111 RAMS detection decreased by feeding 40% MDGS but not by feeding the corresponding corn bran diet. Detection of EHEC O157 or O145 was not associated with dietary factors. Feeding 40% MDGS increased the probability for carriage of some EHEC serogroups but decreased probability of others, which indicated that EHEC serogroups have different risk factors associated with feeding MDGS and little association with dietary fibre., (© 2017 Blackwell Verlag GmbH.)

Pens of cattle with high Escherichia coli O157:H7 (STEC O157) prevalence at harvest may present a greater risk to food safety than pens of lower prevalence. Vaccination of live cattle against STEC O157 has been proposed as an approach to reduce STEC O157 prevalence in live cattle. Our objective was to create a stochastic simulation model to evaluate the effectiveness of pre-harvest interventions. We used the model to compare STEC O157 prevalence distributions for summer- and winter-fed cattle to summer-fed cattle immunized with a type III secreted protein (TTSP) vaccine. Model inputs were an estimate of vaccine efficacy, observed frequency distributions for number of animals within a pen, and pen-level faecal shedding prevalence for summer and winter. Uncertainty about vaccine efficacy was simulated using a log-normal distribution (mean = 58%, SE = 0.14). Model outputs were distributions of STEC O157 faecal pen prevalence of summer-fed cattle unvaccinated and vaccinated, and winter-fed cattle unvaccinated. The simulation was performed 5000 times. Summer faecal prevalence ranged from 0% to 80% (average = 30%). Thirty-six per cent of summer-fed pens had STEC O157 prevalence >40%. Winter faecal prevalence ranged from 0% to 60% (average = 10%). Seven per cent of winter-fed pens had STEC O157 prevalence >40%. Faecal prevalence for summer-fed pens vaccinated with a 58% efficacious vaccine product ranged from 0% to 52% (average = 13%). Less than one per cent of vaccinated pens had STEC O157 prevalence >40%. In this simulation, vaccination mitigated the risk of STEC O157 faecal shedding to levels comparable to winter, with the major effects being reduced average shedding prevalence, reduced variability in prevalence distribution, and a reduction in the occurrence of the highest prevalence pens. Food safety decision-makers may find this modelling approach useful for evaluating the value of pre-harvest interventions., (© 2013 Blackwell Verlag GmbH.)