Some observations on the value of the infectious bronchitis haemagglutination inhibition test in the field

The response of commercial broilers vaccinated against infectious bronchitis (IB) in a conventional manner was examined by the IB haemagglutination inhibition (HI) test and correlated with the clinical picture. On this basis, differences in serum titres were observed which were significant in the diagnosis of clinical disease. Results in vaccinated broiler breeders indicated similar differences in titre patterns which were related to the clinical history of the flock, but some evidence of titre variation due to cycling of vaccine virus in the flocks made interpretation more difficult. The test is a rapid and simple serological aid to diagnosis of IB.