Newcastle disease (ND) is among the most common and deadliest poultry diseases worldwide. Thermostable Newcastle disease virus (NDV) vaccines have been widely used to protect village chickens against ND due to their decreased dependence on cold chains for transport and storage. The NDV4 Heat-Resistant (NDV4HR) vaccine is an apathogenic, heat-resistant, live vaccine that can induce immunity in chickens. In this study, 60 one-day-old Arain local hybrid broilers were divided into three groups of 20. Group A had the usual vaccination program in broiler flocks (seven days old: B1 type by eye drop and ND killed vaccine intramuscularly; 18 and 28 days old: LaSota strain orally). Group B did not receive any vaccine, and group C received the NDV4HR vaccine orally, six times from the first day to the 35th day of rearing. All groups were nasally challenged with acute Newcastle virus (genotype VIId) on the 35th rearing day. Regarding the hemagglutination inhibition serum antibody titer of the birds after the challenge, group B had the highest (7.12±1.05), and group C (6.37±1.31) had a higher titer than group A (6±1.22). After the challenge with the Newcastle virus, the necropsy findings and clinical symptoms of the disease were almost similar in groups A and C. Group B showed the most signs, with higher casualties than other groups. Regarding weight gain, group C had the highest weight at the end of the study (2204±106). On the second day after the challenge, groups A and B had virus shedding through the trachea and cloaca, while group B shed the virus only through the trachea. Furthermore, on the seventh day after the challenge, group A shed the virus through the cloaca, whereas group B did it through the trachea and the cloaca. On the other hand, there was no virus shedding in group C. This study showed that the NDV4HR vaccine provokes an antibody response that protects the birds against a virulent virus challenge.

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