Abstract
Dairy cattle in two commercial Holstein herds were randomly selected to be vaccinated twice with J5, at approximately 60 days and 28 days before the expected calving date, or to be untreated controls. Based on whether milk production changed following clinical mastitis or whether cows were culled or died within 30 days after onset, 51 mastitis cases were classified as severe or mild. J5-specific antibody responses were evaluated by enzyme-linked immunosorbent assay of all 32 severe and 19 mild cases. The amounts of J5-specific immunoglobulin M (IgM), IgG1, and IgG2 antibodies in sera from the 27 J5 vaccinates were compared with those of the 24 controls. At drying off (before J5 vaccination), all cows had similar amounts of J5-specific antibody. Immediately after calving (approximately 28 days after the second vaccination), J5 vaccinates had significantly higher production of J5-specific IgG1 and IgG2 than controls. When cows were tested following clinical mastitis, none of the three antibody classes differed significantly between the controls and the vaccinates. Vaccinates that contracted Escherichia coli mastitis had 75% less milk loss than controls. The cows that contracted clinical mastitis later in lactation, the unvaccinated controls, and those infected with E. coli had more milk loss following mastitis. The hazards of being culled for all reasons and of being culled for mastitis were significantly lower for J5 vaccinates. Vaccination with J5 was associated with protection against milk production loss and culling following clinical mastitis, and it was also significantly associated with changes in J5-specific IgM, IgG1, and IgG2 antibodies in sera of vaccinated cows.