The efficacy of infectious bronchitis virus vaccination in the field: association between the α-IBV IgM response, protection and vaccine application parameters
Résumé
Infectious bronchitis virus (IBV) is, in spite of vaccination(s), still a major cause of respiratory problems in broilers and of poor egg production in breeders and layers in many parts of the world. A possible cause of the insufficient protection induced by vaccination(s) is an inadequate application of the vaccine. This paper reports the results of two field studies. In a first field study, the results of the α-IBV IgM ELISA on post-vaccination sera were compared with the efficacy of the IBV vaccination against homologous challenge of the same broilers. The results showed that groups with at least 50% positive sera in the IgM ELISA at 10 days post vaccination had a high level of protection against challenge. Most groups of broilers with a low level of IgM ELISA positives had mostly a low or moderate level of protection against challenge. In a second field study, the IgM response to IBV vaccination was compared to detailed information of the vaccination process of 360 spray-vaccinated flocks of about 2-week-old broilers, layer pullets, broiler breeders and broiler grand parents. The information included parameters such as flock size, type of chicken, housing, age of the chicken, application route, vaccine, dosage, water quantity and temperature, ventilation and light management, combination with other vaccines and temperature of the house. The aim was to identify factors that might be associated positively or negatively with the IgM response and thereby with the expected level of protection against homologous challenge under field conditions.
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