The Influence of Vaccination of Broiler Chickens and Turkeys with Live Attenuated Vaccine on Population Properties and TRT Vaccination Efficacy.

Colibacillosis is one of the major causes of economic losses in the poultry industry. Vaccination against is attracting increasing interest. The aim of the study was to evaluate the influence of vaccination with live, gene-deleted vaccine on the structure and properties of field population and its potential impact on TRT vaccination efficacy in broiler chickens and turkeys. We performed three independent experiments on farms: (1) with antibiotic-free broiler chickens, (2) with conventional broiler chickens and (3) with broiler turkeys. In experiment 1, we have recorded an approx. 0-15% prevalence of multi-susceptible strains in the first production cycle. Starting from production cycle number two, after vaccination introduction, successive significant increases in susceptibility emerged, reaching 100% of strains at the end of production cycle 3. Increased susceptibility remained for three production cycles after vaccination withdrawal. In experiments 2 (2 production cycles) and 3 (1 production cycle), we recorded similar tendencies of susceptibility profile change. In experiments 1 and 2, the population count was lower after vaccination. In experiments 2 and 3, no negative influence of vaccination on the level of specific antibodies against TRT was recorded.