Evaluation of Newcastle Disease antibody titers in backyard poultry in Germany with a vaccination interval of twelve weeks.

Newcastle Disease (ND) is a viral disease spread worldwide with a high impact on economy and animal welfare. Vaccination against Newcastle Disease is one of the main control measures in countries such as Germany with endemic occurrence of Newcastle Disease virus in the free ranging bird population. The German Standing Veterinary Committee on Immunization (StIKo Vet) recommends to revaccinate chickens at intervals of six weeks against Newcastle Disease with attenuated live vaccines via drinking water or spray in line with the SPCs (Summary of Product Characteristics) of current vaccines. However, it is still common practice to revaccinate only every twelve weeks because the SPCs of former vaccines proposed a revaccination after checking the antibody titer which based on practical knowledge was typically sufficient for twelve weeks. The aim of this study was to evaluate if a vaccination interval of twelve weeks against Newcastle Disease under field conditions results in sufficient seroconversion to protect flocks. Antibody titers of 810 blood samples from 27 backyard flocks of chickens were analyzed by ELISA- and HI-tests between 69 and 111 days after vaccination of the flocks with attenuated live vaccines of the ND strain Clone 30. Furthermore, data on the flocks such as breed, sex and age were collected through a questionnaire. In this study a sufficient antibody titer was found in 26 of these flocks. Therefore, a vaccination interval of every twelve weeks with the live vaccines tested is suitable for a vaccination protocol against Newcastle Disease. The lack of seroconversion of one flock also emphasizes the need for regular vaccination monitoring by serological testing and re-evaluation of the vaccination process if needed.