Passively Transferred Immunity in Newborn Calves, Rate of Antibody Decay, and Effect on Subsequent Vaccination with Modified Live Virus Vaccine

The passive immunity transferred to calves via colostrum containing antibodies to infectious bovine rhinotracheitis virus (BHV-1), bovine viral diarrhea virus (BVDV) 1, BVDV 2, parainfluenza-3 virus (PI-3V) and bovine respiratory syncytial virus (BRSV) was investigated to determine half-life of antibody, time to seronegative and effect on immunization. Thirty dairy calves were fed colostrum from non-pooled sources. Serum samples were obtained at the following times: prior to colostral feeding for BVDV isolation; two days of age to measure peak or near peak serum IgG and antibody to the five viruses in this study; and 30 days of age, and approximately 30-day intervals thereafter to assess colostral antibody decay and/or serologic response to vaccine antigen. Antibody titers to each of the five viruses were determined using viral neutralization tests. The mean titers in the day 2 serums were: 17.0 to IBRV; 79.1 to BVDV 1; 297.1 to BVDV 2; 479.2 to PI-3V; and 347.5 to BRSV. The mean half-life of antibodies to each virus was: IBRV, 12.7 days (d); BVDV 1, 20.5 d; BVDV 2, 20.5 d; PI-3V, 21.7 d; and BRSV, 28.1 d. The calculated time to seronegative status for each virus was: IBRV, 65.1 d; BVDV/1, 117.7 d; BVDV/2, 94.0 d; PI-3V, 183.8 d; and BRSV, 200.2 d. The time to seronegative status was dependent on amount of antibody absorbed and antibody decay rate. Calves were vaccinated as viral antibody titers either reached 0, or in the presence of waning antibodies, with a modified live virus vaccine containing IBRV, BVDV 1, BVDV 2, PI-3V, and BRSV immunogens. The active immune response (seroconver- sion) was dependent on the virus and sion) was dependent on the virus and amount of passive antibodies present at vaccination.