Virus-neutralization versus agar-gel precipitin tests for detecting serological response to infectious bursal disease virus.

The virus-neutralization (VN) test was found much more sensitive than the agar-gel precipitin (AGP) test for detecting prior exposure to infectious bursal disease (IBD). Many sera that were negative in the AGP test were found to have VN antibodies, and virtually all sera in a commercial flock were free of precipitin but had VN titers. VN titers varied widely on a flock basis, and revaccination of an 8-month-old flock through the drinking water did not alter the antibody titers. Inoculation of maternally immune chicks at 7 days of age with IBD virus resulted in a good serologic response by both the AGP and VN tests.