Efficacy of Vaccination Programmes Using Two Commercial Live Infectious Bronchitis Vaccines against a Field Irfib 32 Strain

The effectiveness of two commercial infection bronchitis vaccines including H120 and 4/91 was evaluated in broiler chickens challenged with IBV strain IRFIB32 in different vaccination programmes. For this purpose, 180 day-old Cobb 500 chicks were randomly divided in six treatment groups. Four chicks in each group were humanely sacrificed at 2, 4, 6 and 10 days post challenge for evaluating ciliary activity and molecular detection of the challenged virus in trachea, lung, kidney, testis or oviduct tissues and faeces. A very mild depression and short transient conjunctivitis were observed in challenged vaccinated groups in comparison with unvaccinated challenged chicks. Body weights of the birds in the treatment groups were not significantly different (P>0.05) at the end of the experiment. In ciliostasis test, percentage of protection against chicken groups 2 (4/91, 4/91), 4 (H120/4/91) and 5 (H120, H120) was 85%, 76% and 58%, respectively. All vaccinated challenged chicken groups showed protection against challenge virus, but in the homologue vaccinated birds (4.91, 4.91) protection was more efficient (P<0.05). Antibody titre in H120 vaccinated unchallenged birds (group 1) was lower than in 4.91 vaccinated unchallenged birds (group 6). The birds in groups 4 and 5 had the highest titre of antibody in ELISA (P<0.05) at the end of the study and the difference between these two groups was also significant (P<0.05). The challenged virus were detected in faeces and oviduct or testis tissues up to 10 days post challenge, while the tracheal tissue showed it up to 4 days post challenge. On the basis of viral shedding, vaccination of chicks in groups 2, 4 and 5 provided statistically greater protection than the non-vaccinated control group (P<0.05), 88.75%, 92.5% and 85%, respectively. We conclude that an efficient protection occurred in three different vaccination programmes; however, the birds challenged with homologous virus vaccine resulted in more effective protection.