摘要： 使用SPF雏鸡进行鸡传染性囊病二价活疫苗的攻击保护滴度的测定。SPF雏鸡14日龄免疫，于免疫后7d、8d、9d、10d、12d、14d采血进行IBD中和抗体的测定，同时分别进行标准I型强毒CJ801株和标准变异株强毒1084A株的攻击，建立抗体滴度与攻击保护率之间的直线回归方程。二价苗免疫后14dIBD中和抗体滴度达到2968（GMT），其对CJ801株和1084株的攻击保护率分别为89.21%和82.59%，从而表明在免疫抗体达到2968时，免疫鸡表现对IBD强毒良好的攻击保护效果，并将此抗体滴度暂定为鸡传染性囊病二价活疫苗的中和保护滴度。

关键词: 鸡传染性囊病二价活疫苗, 中和抗体滴度, 攻击保护率

Abstract: A detection of protective titers of a bivalent live IBD vaccine was conducted using SPF chicks. The chicks were vaccinated at 14 days of age, and were bled and their blood samples and sera collected for the detection of neutralizing antibodies to IBDV in a virus-neutralization (VN) assay and simultaneously challenged with either a standard serotype Ⅰ virulent IBDV strain CJ801 or a virulent variant IBDV strain 1084A at 7, 8, 9, 10, 12, 14 days post-vaccination, respectively. A rectilinear regression equation between IBD antibody titers and protective rates was established. When the VN antibody titer (GMT, geometric mean titer for vaccinated chicks with the vaccine) increased by 2968, the vaccinated chicks had 89.21% and 82.59% protections against the challenges of strains CJ801 and 1084A, respectively. Consequently, the IBD antibody titer of 2968 (GMT) was tentatively regarded as a protective neutralizing antibody titer resulted from the vaccine against virulent IBD viruses.

Key words: Bivalent live infectious bursal disease vaccine, VN antibody titers, Protective rates