In the present study, 360 male day-old broiler chicks were used to determine the effect of mixed live vaccines of Newcastle disease (ND) and infectious bronchitis (IB) on serum and local antibody responses to IB. Chicks were randomly divided into 12 treatment groups of 3 replicates and reared for 40 days on floor pens. Groups 1 to 5 received mixed ND and IB vaccine. Groups 7 to 11 received IB vaccine alone and regarded as positive controls. Group 6, that received ND vaccine only, and group 12, that received no vaccine, were considered as negative controls. Antibody titer against IB in the nasal washings and sera was measured using enzyme-linked immunosorbent assay (ELISA). The chickens were inoculated with IB live vaccine (strain H120) with or without ND live vaccine by means of an eye dropper. Serum samples obtained on the 19th and 29th day of age and serum samples, as well as nasal washings, collected on day 40, were used to determine systemic and local antibody responses to IB. On the 40th day of age, tracheal samples were also collected to study the probable pathologic lesions due to the effect of live vaccines used. There was no significant difference in systemic antibody response (SAR) among all groups measured on the 19th day. On the 29th and 40th day of age, SAR of the negative control groups was significantly (P<0.05) different from those received IB vaccine. On the 40th day, nasal washings showed higher antibody titer as compared to the systemic antibody titer (P<0.05). The pathologic lesions in groups received mixed vaccine were higher than groups received IB vaccine alone or the control groups. Mortality rate, weight gain and food conversion ratio were not significantly different among groups studied. Despite the observations that mixed live IB and ND vaccination resulted in a higher antibody response as compared to the single IB vaccination, yet this program could not be ecommended to use in farm due to higher pathologic lesions in trachea.

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