A study was conducted for quantification of antibodies to haemagglutinating viruses such as AIV (H9N2 and H7N3), NDV and IBV in vaccinated poultry flocks. A total of 198 serum samples from different commercial broiler and layer farms in Lahore, Pakistan, were checked for their serological statuses. Haemagglutination inhibition (HI) test was performed to determine the titer of serum antibodies against the above mentioned viruses. It was observed that 25 and 44% samples were positive for H7N3 and H9N2 in broilers, respectively. The seropositivity of H7N3 and H9N2 in serum samples of commercial layers were 66 and 94%, respectively. It was recorded that 96% of the samples in broilers and 100% of those in layers, were found seropositive for antibodies against NDV. Moreover, 69 and 86% were seropositive for IBV in broilers and layers, respectively. Calculated geometric mean titers for groups of 0-2, 2-4 and 4-6 weeks of age were found to be 36.8, 78.8, and 111.4 for H9N2; 48.5, 157.6, 222.9 for NDV; and 97, 84.4, 111.4 for IBV, respectively. It was concluded that the samples were not having protective antibody titers indicating unsuccessful vaccination practiced in these poultry farms which may lead to significant economic losses.
Key words: Avian influenza virus, Newcastle disease, bronchitis virus, haemagglutinating.