Replacement of challenge procedures in the evaluation of poultry vaccines.

Vaccination of poultry flocks, especially parent flocks, is often performed with the intention of protecting the progeny via maternal antibodies during the first weeks of life. The efficacy of this vaccination schedule, more precisely described as induction of indirect protection, is normally proven by challenging the chickens. To avoid the challenge, some trials were performed, with the intention of establishing a correlation between antibody titres of vaccinated hens, embryonated eggs, and hatched chickens. The parent flocks were divided into several groups which were vaccinated either with Infectious Bursitis (IBD) vaccine or with Newcastle Disease (ND) vaccine. An acceptable correlation could be established. A well described standard or reference serum and a standardized and reproducible test procedures could be used in different laboratories. This approach allows serological test results to be compared. The possible parameters for the reference sera, including antibody titre, protein content and additional parameters, are discussed.