Results of a Salmonella enteritidis vaccination field trial in broiler-breeder flocks in the Netherlands

From August 1995 until December 1997, the effect of adding Salmonella enter itidis (SE) vaccination to a certified standardized biosecurity program in a situation of increased infection risk was examined in a field trial in Th e Netherlands. In this field trial, two groups of broiler-breeder flocks wi th increased infection risk were vaccinated, one group with VAC-T/TALOVAC(R ) logSE(group A) and the second group with SALENVAC(R) (group B). The deter mination of increased infection risk in groups A and B was based on an SE i nfection history; flocks were either previously infected and treat ed (PIT) or had other risk factors than previously infected and treated (OPIT). SE infections in both vaccinated groups were assessed by monitoring according to the Dutch salmonella control program. Under field conditions, designation of a vaccinated and a control group on the farm was not possible. In the same period as the vaccinated groups, 608 nonvaccinated flocks (group C) were hatched and monitored according to the Dutch salmonella control program. The flock level occurrence of SE infection in the vaccinated groups was com pared with the flock level occurrence of SE infection in the nonvaccinated group on the basis of comparability of infection risk. In group C, whether or not flocks had infection risk PIT was known and for risk factor OPIT, on ly whether or not a flock had been placed on a previously contaminated farm (= risk of reinfection) was known. The proportion of SE-infected flocks with risk factor PIT in the vaccinated groups was not significantly different from that in the nonvaccinated grou p C. Only the proportion of SE-infected flocks with a risk of reinfection i n the vaccinated group B (0) was significantly lower (P = 0.02) than in the nonvaccinated group C (18%). The fact that no significant result was found in favor of group A is because of the small number of flocks in this part of the study On the basis of the conditions of the setup of this trial, it can only be c oncluded that there is an indication that vaccination contributes in the re duction of SE reinfection in broiler breeder flocks.