The parameters controlling IgG antibody responses induced by vaccination against bovine respiratory syncytial virus (BRSV) were investigated in 463 Holstein-Charolais crossbred cattle. Pre- and post-vaccination sera were tested by enzyme linked immunosorbent assays (ELISA) for BRSV-specific IgG and IgG2. Year-of-birth, age, sex and pre-existing antibody were significant sources of variation for IgG responses. Pre-vaccination, progeny with a higher proportion of Holstein genes had higher total BRSV-IgG. By Day 35 post-vaccination, heritabilities peaked at 0.26 for total BRSV-IgG and 0.36 for BRSV-IgG1. There was no evidence for interbreed differences between Holstein and Charolais calves, post-vaccination. These results suggest that calf-sire has a major heritable influence on serum IgG levels following BRSV immunisation.