A Randomized Longitudinal Trial to Test the Effect of Regional Vaccination Within a Cattle Feedyard on Escherichia coli O157:H7 Rectal Colonization, Fecal Shedding, and Hide Contamination

We tested the efficacy of vaccinating all cattle within a region of a cattle feedlot using a two-dose regimen of a vaccine against type III secreted proteins of Escherichia coli O157:H7. Cattle (n = 504) were randomly assigned to 63 pens (8 steers/pen) within 3 treatment regions of the feedyard. All pens within each region were assigned: (1) two doses of vaccine (ALLVAC), (2) two doses of adjuvant as placebo (NOVAC), or (3) commingled vaccination (HALFVAC), four of eight cattle in each pen receiving two doses of vaccine, and the others adjuvant. Binary outcomes were (1) fecal shedding of E. coli O157:H7 42, 63, and 84 days postvaccination (dpv), (2) hide contamination 42, 63, and 84 dpv, and at the abattoir 85 dpv, and (3) colonization of the terminal rectal mucosa at the abattoir 85 dpv. For each outcome, multilevel logistic regression tested the effect of regional vaccination (ALLVAC vs. NOVAC), and compared commingled vaccinated versus placebo-treated cattle within HALFVAC pens. For fecal shedding, regional vaccine efficacy of ALLVAC compared to NOVAC pens was 63% (OR = 0.34, p = 0.0009), similar to vaccine efficacy of 52% for vaccinated cattle compared to placebo-treated cattle within HALFVAC pens (OR = 0.48, p = 0.014). For hide contamination, vaccine efficacy was 55% for regional vaccination of cattle in ALLVAC pens compared to NOVAC pens (OR = 0.43, p = 0.014). However, commingling vaccinated and placebo-treated cattle was not protective of hide contamination (OR = 0.67, p = 0.33). Colonization of cattle at the abattoir was not different among vaccinated and placebo-treated cattle (p = 0.63). We concluded that the two-dose vaccine regimen effectively reduced E. coli O157: H7 fecal shedding and hide contamination, and that vaccination of cattle within regions of the feedyard provided greater protection against hide contamination than commingling vaccinates and nonvaccinates.