Antibody levels against bovine respiratory syncytial virus in Belgian White Blue calves and young cattle in autumns 1996 and 1997

Severe clinical signs, associated with bovine respiratory syncytial virus ( BRSV) infection, mainly occur in cattle of less than 1 year old. The aim of this field study was then to determine the antibody levels against BRSV in 927 cattle of this age group before the winter season which is favourable to natural BRSV contamination. With regards to the serological results, cat tle can be divided in 2 groups. The first group includes carves less than 4 months old with maternal antibodies which decline in the same way with the age rise. The seronegative animals of 5 to 12 months old build the second group up. The presence of specific-BRSV maternal antibodies in calves less than 4 months old raise several questions about a possible protective effec t of these antibodies against BRSV disease, the immune response induced by a BRSV infection, the BRSV vaccination of very young carves and the serolog ical diagnosis of BRSV infection.