Decay of maternal neutralizing antibodies against foot and mouth disease virus (FMDV) in the calves born to the dam vaccinated for FMD during 80-110 days of gestation.

Passive immunity against foot and mouth disease virus (FMDV) is important till the time of primary vaccination as it causes high mortality in the calf. Hence, it is necessary to determine the vaccination window of the dam during the pregnancy. Accordingly, serial sera were collected at monthly interval (0-5 months) from the calves (n = 15) whose dams were last vaccinated during 80-110 days of pregnancy with an oil-adjuvanted inactivated FMD vaccine covering serotypes O, A, and Asia1. First blood sample from the calf was collected 2-3 days post-birth while blood sample was collected from the dam 3-5 days before expected calving. Virus neutralization (VN) test was performed and the resulting neutralizing antibody titer was compared with the expected protective titer. One sample t test revealed that the calves had passive immunity at birth for all the three serotypes (P > 0.05). Mixed model ANOVA indicated that the VN titer declined significantly by 2 months for serotype O and by 3 months for other two serotypes (P < 0.05). Antibody response to serotype O was highly variable among the calves as evidenced by a random effect of 73%. Though a positive correlation was expected in the VN titer between the dam and calf, no such result was found for any of the three FMDV serotypes. It was concluded that the protective window of FMD vaccination of dam is beyond 110 days for all the three serotypes of FMDV to confer adequate passive immunity to the calf.