COMPARISON OF DIFFERENT COMPUTATIONAL METHODS FOR MEASURING ANTIBODIES TO AVIAN INFECTIOUS-BRONCHITIS VIRUS IN SINGLE SERUM DILUTION

Twenty-eight one-day-old chickens with infectious bronchitis virus (IB V) maternal antibodies were immunized with strain H120 (Bronchovac-I, Phylaxia) in spray form. The chickens were kept in an isolator. On day 42 and 56 the chickens were immunized with IBV strain M41 (10(3.0)EID 50/0.1 ml). Serum antibody titres were measured by both serial dilutio n and single dilution ELISA on day 42, 56 and 76. ''Twice negative ave rage'' (TNA), ''sample to positive'' (SP) and ''subtraction method'' ( SM) titres were calculated from the serially diluted sera, and SP and SM titres were calculated from the single dilution. Titres obtained by the different methods showed a good correlation for sera of low, medi um and high antibody levels. The authors recommend the use of the sing le dilution method.