ANTIBODY TITRES IN BROILERS OF INFECTIOUS BRONCHITIS VIRUS STRAINS 4/91 AND MASSACHUSETTS IN THAILAND

Abstract

Thirty, one-day-old broilers were divided into 3 groups, 10 birds each. Group 1 was vaccinated twice with a live infectious bronchitis virus vaccine, (IBV)-serotype Massachusetts, strain H120 when one day old and a live IBV-strain Massachusetts vaccine when ten days old. Group 2 was vaccinated once with a live IBV-strain Massachusetts vaccine when ten days old. Group 3 were non-vaccinated
controls. Blood samples were taken from birds on days 1, 10, 21, 28, 35 and 42. Samples were tested by a virus neutralization(VN) test, for strains 4/91 and Massachusetts(M41) neutralizing antibodies and were tested by an enzyme-linked immunosorbent assay(ELISA) for IBV antibodies. Samples from broiler farms which were vaccinated once or twice with a live IBV-serotype Massachusetts or strains H120 and Massachusetts vaccines were tested in the same manner on days 28, 35 and 42. The results revealed that experimental broilers which were vaccinated twice with serotype  Massachusetts vaccine had higher Massachusetts VN titres than broilers which were vaccinated once. Both vaccinated groups had low 4/91 VN titers. Samples from two broiler farms had levels of Massachusetts and 4/91 VN titres as well as IBV ELISA titres higher than those in the experimental groups. Base on the serological observations, broilers from the two farms may have been infected with field IBV and it still remains uncertain whether IBV strain 4/91 is present in Thailand.