摘要
[ Objective] To study the correlation between HI titer and protection against IBV challenge in SPF layers. [ Method ] SPF layers were randomly divided into four groups, namely group A1, A2, B1 and B2. The group A1 was immunized with H120 live vaccine. The group A2 was first immunized with H120 live vaccine and later boosted with ND-IB-EDS trivalent inactivated vaccine. The group B1 was used as unimmunized chal- lenge control. The group B2 was kept as unimmunized unchallenged control. The blood samples were taken prior and post-vaccination at intervals and HI tests were conducted. At the laying peak, the group A1, A2 and B1 were challenged with IBV M4t virulent strain. The clinical features and egg production of layers were monitored and recorded. [Result] After 30 d post vaccination with H120 live vaccine, the HI titer reached 4.45 log2; after 30 days boosting with ND-IB-EDS trivalent inactivated vaccine, the HI titer reached to 7.35 log2. Before challenge, HI antibody titer in group A1, A2, B1 and B2 were respectively 4.24 log2, 7.40 Iog2, 2.10 log2 and 2.10 log2. After challenge, chickens in unimmunized challenge control group B1 showed respiratory symptoms, egg production dropped by 30.9%, and they produced more soft-shelled, no-shelled or abnormal eggs. In the group A1, some chickens had light respiratory symptoms and egg production dropped by 11.7%. In the group A2, the egg production of all chickens was as normal as the group B2. [ Conclusion] When the HI titer was over 6 log2, challenge by virulent virus had no impact on egg produc- tion; when the HI titer was 5 log2, 4 log2 and less 3 log2, egg production dropped by 6.0%, 11.3% and 29.6%, respectively. Thus, the HI anti- body level in chickens has close correlation with protection against IBV challenge.
[ Objective] To study the correlation between HI titer and protection against IBV challenge in SPF layers. [ Method ] SPF layers were randomly divided into four groups, namely group A1, A2, B1 and B2. The group A1 was immunized with H120 live vaccine. The group A2 was first immunized with H120 live vaccine and later boosted with ND-IB-EDS trivalent inactivated vaccine. The group B1 was used as unimmunized chal- lenge control. The group B2 was kept as unimmunized unchallenged control. The blood samples were taken prior and post-vaccination at intervals and HI tests were conducted. At the laying peak, the group A1, A2 and B1 were challenged with IBV M4t virulent strain. The clinical features and egg production of layers were monitored and recorded. [Result] After 30 d post vaccination with H120 live vaccine, the HI titer reached 4.45 log2; after 30 days boosting with ND-IB-EDS trivalent inactivated vaccine, the HI titer reached to 7.35 log2. Before challenge, HI antibody titer in group A1, A2, B1 and B2 were respectively 4.24 log2, 7.40 Iog2, 2.10 log2 and 2.10 log2. After challenge, chickens in unimmunized challenge control group B1 showed respiratory symptoms, egg production dropped by 30.9%, and they produced more soft-shelled, no-shelled or abnormal eggs. In the group A1, some chickens had light respiratory symptoms and egg production dropped by 11.7%. In the group A2, the egg production of all chickens was as normal as the group B2. [ Conclusion] When the HI titer was over 6 log2, challenge by virulent virus had no impact on egg produc- tion; when the HI titer was 5 log2, 4 log2 and less 3 log2, egg production dropped by 6.0%, 11.3% and 29.6%, respectively. Thus, the HI anti- body level in chickens has close correlation with protection against IBV challenge.
