Abstract   

A total of 2185 blood samples obtained from 110 poultry flocks were analyzed for antibodies to various strains of avian infectious bronchitis virus (IBV). These samples were obtained from commercial broiler, broiler-breeder, commercial layer and layer breeder flocks located in various geographical regions of Pakistan. The flock histories in terms of production performance, growth patterns and LB disease prevalence, vaccines and vaccination programs were recorded. Samples of blood from locally bred desi (native) birds and pheasants were also analyzed. These samples were primarily collected from flocks which had experienced low production, misshaped eggs and mortality in the near past. All the serum samples were analyzed using haemagglutination-inhibition (HI) test. This study indicated the presence of antibodies to various IBV types such as Arkansas, Massachusetts-4 1 (M-41), JMK, D-274 and D- 1466. It was further observed that the breeder and commercial flocks which did not receive any killed or live IBV vaccination had significant titres of humoral HI antibodies indicating that various field IBV types were circulating in those flocks. The presence of IBV antibodies in unvaccinated flocks was higher in areas where poultry farms were located in clusters or where multiple age groups were housed.