Primary Newcastle disease vaccination of broilers: comparison of the antibody seroresponse and adverse vaccinal reaction after eye-nose drop or coarse spray application, and implication of the results for a previously developed coarse dry powder vaccine.

To compare antibody seroresponse and adverse vaccinal reaction induced by Newcastle disease (ND) vaccination after eye-nose drop or coarse spray, groups of SPF broiler hens were vaccinated at day 4 (day of hatch is day 0) and intratracheally inoculated with Escherichia coli at day 11. Body weight gain (BWG) was assessed between day 4 and day 18; colibacillosis lesions and serum antibodies were determined at day 18. Meaningful comparison requires similar vaccine uptake. Vaccine virus loss during spray relative to eye-nose drop, which was assessed by comparing the results of endpoint titrations, was 3 log10. Colibacillosis lesions in birds spray vaccinated with 106.4 EID50/chicken were significantly more severe (P < 0.05), compared to those in birds eye-nose drop vaccinated with 103.4 EID50/chicken, while the seroresponse was slightly but significantly (P < 0.05) stronger. Colibacillosis lesion scores inversely paralleled BWG. It is concluded that: (1) There is room to improve the coarse ND vaccine spray used regarding adverse vaccinal reaction, while maintaining a sufficient immune response. This is also applicable to the coarse ND powder vaccine studied in previous research, which induced similar antibody response and adverse vaccinal reaction as the spray vaccine used here. (2) The vaccine virus dose influences the colibacillosis susceptibility at seven days post vaccination, as the dynamics of the vaccine virus infection is likely dose-dependent. (3) Low vaccine virus doses likely result in heterogeneous vaccine-take followed by vaccine virus spread from vaccine shedding birds to their non-vaccine virus infected flock mates ("rolling vaccinal reaction").