Abstract
Thirteen bovine leukemia virus- (BLV-) negative and 22 BLV-positive Holstein cows were immunized with J5 Escherichia coli bacterin at dry off, three weeks before calving, during the second week after calving, and three weeks after the third immunization. Serum was collected before the initial immunization, immediately before the third and fourth immunizations, and 21 days after the fourth immunization. Anti-J5 E. coli IgM, IgG1, and IgG2 titers were determined by ELISA. Anti-J5 E. coli IgM titers did not differ significantly (P = .98) between groups. Increases in anti-J5 E. coli IgG1 titers were higher in the BLV-negative cows (P = .057). Geometric mean anti-J5 E. coli IgG2 titers increased fourfold in the BLV-negative cows, which was significantly higher (P = .007) than the twofold increase in the BLV-positive cows. Cattle infected with BLV may have impaired serologic responses following immunization with J5 bacterin, and response may differ according to antibody isotype.