Antibody titer against bovine respiratory syncytial virus in colostrum-fed dairy calves born in various seasons.

OBJECTIVE: To determine antibody titer against bovine respiratory syncytial virus (BRSV) in dairy calves on farms and to investigate whether passively acquired antibody titers differ in calves born in various seasons. SAMPLE POPULATION: Serum samples from 129 colostrum-fed replacement calves in 8 dairy herds. PROCEDURE: A standard ELISA was used to determine BRSV-specific antibodies in serum samples obtained monthly, and antibody titers for calves born in various seasons were compared. RESULTS: BRSV-specific antibody titer in colostrum-fed dairy calves decreased to undetectable values at 3 to 4 months old. Calves born in winter generally had lower titers, compared with those for calves born in other seasons (P < 0.05). Titers in calves born in seasons other than winter did not differ. CONCLUSIONS AND CLINICAL RELEVANCE: Calves born in winter generally have lower BRSV-specific antibody titers, which may be caused by generally lower antibody titers in colostrum or by factors influencing colostrum intake.