Effectiveness of specific immune response of broiler chicken body during homologous vaccination against avian infectious bronchitis

Avian infectious bronchitis of chickens is one of the most common viral infections that cause huge economic damage to broiler poultry farming. Economic damage caused by infectious bronchitis is mainly associated with high mortality of broiler chickens under the age of 30 days. An important condition for ensuring epizootic well-being regarding infectious bronchitis in chickens is the effectiveness of specific prevention. The high variability of the virus and the appearance of new serotypes necessitate systematic serological control of the intensity of specific immunity and constant changes in vaccination programs. The research findings on the effectiveness of specific prevention of infectious bronchitis in broiler chickens based on the use of a homologous live vaccine containing the H-120 strain of the Massachusetts serotype showed that vaccination of broiler chickens at a daily age by spray method followed by revaccination on the 19th days of their life by the method of drinking provides a satisfactory level of specific protection. The value of the average antibody titers in broiler chickens of all groups when using the infectious bronchitis virus (IBV) vaccine reached the level of the arithmetic mean titer of 2144.25 (log2 9.25 ± 1.54), the geometric mean titer of 1729.25. The minimum number of antibodies was found in 27 (29.35%) samples (from 298 to 943); the average number - in 60 (65.22%) samples (from 1121 to 5835), and the maximum was in five (5.43%) samples (from 6232 to 6322). The intensity index of group-specific immunity averaged 94.56%. The coefficient of variation of the average antibody titers was 57.22 ± 5.20 (p < 0.05). High level of group immunity (from 82.60% to 100.00%) after vaccination protects the broiler chicken population from the age of one day to the end of the productive period. The variation of antibody titers from 298 to 6322 indicates an uneven level of immune response which may affect the spread of the disease among broiler chickens. Adjusting the timing and schemes of revaccination for replacement young chickens will increase the effectiveness of immunization and ensure stable blocking against infectious bronchitis.