Thermoresistant Newcastle disease vaccine effectively protects SPF, native, and commercial chickens in challenge with virulent virus

Abstract Background Due to the more stability and a better homogenecity in immune response, the use of thermoresistant vaccines in different chicken types has been increased. Objective This study aimed to evaluate the efficacy of a newly developed Newcastle disease vaccine (ND.TR.IR) originating from I‐2 strain in specific pathogen‐free (SPF) and native and broiler chickens. Methods Following determination of pathogenicity indices on the candidate seed, three efficacy examinations were conducted. In the first experiment, 120 1‐day‐old SPF chickens were randomly allocated to six groups and either vaccinated with ND.TR.IR via eye drop at 1, 7, and 21 days of age (V1, V7, and V21), or considered as non‐vaccinated control groups (C1, C7, and C21). At 20th post‐vaccination day, sera hemagglutination inhibition (HI) antibody titres against ND virus (NDV) were measured and then the chickens were challenged by virulent NDV (vNDV). In the second and third experiments, the efficacy of ND.TR.IR vaccine was compared to routine vaccination program (B1 and LaSota) in native and broiler chickens that were vaccinated at 10 and 20 days of age, respectively. The HI antibody titres were measured on 10, 20, 30, and 40 days of age, and also challenge efficacy test with vNDV was conducted on 30 days of age. Results The studied virus, as a vaccinal seed, complied with the pathogenicity indices of avirulent NDV and molecular identity of I‐2 strain. In the efficacy evaluation trials, the vaccinated chickens had higher HI antibody titres against NDV compared with their corresponding control chickens (p