Safety and efficacy of an aroA-deleted live vaccine against avian colibacillosis in a multicentre field trial in broilers in Morocco

The safety and efficacy of an aroA-deleted live vaccine against avian colibacillosis (Poulvac (R) E. coli) was evaluated in broilers in a multicentre field trial. The trial sites consisted of 18 paired bird houses (randomly assigned to either the vaccination or the control treatment groups) located in 15 farms in three different regions of Morocco. A field dose of vaccine was administered on day of hatch by the spray route. Both clinical and performance parameters were compared between vaccinated and control groups, in which the experimental unit was defined as the individual bird house. No adverse reactions attributable to the vaccine were observed throughout the study. Non-inferiority of the vaccinated bird houses versus the control houses during a 2-week period post vaccination was statistically demonstrated for mortality and average daily weight gain. Vaccine efficacy was confirmed based on significant differences between vaccinated and unvaccinated groups measured for the full duration of the trial, including colibacillosis-like lesions observed at slaughter (1.7 versus 3.5%; P = 0.0054), total mortality (9.3 versus 10.3%; P = 0.0203), average daily weight gain (47.8 versus 46.2 g/day; P = 0.0006), average number of antibiotic treatment days (0.5 versus 2.0; P = 0.0008) and percentage of the birds that was marketed (90.0 versus 89.0%; P = 0.0309). In conclusion, the vaccine was demonstrated to be both safe and efficacious under field conditions.