Vaccination of neonatal colostrum-deprived calves against Pasteurella haemolytica A1

Colostrum-deprived Holstein calves were vaccinated at 2 and 4 wk of age wit h a Pasteurella haemolytica Al culture supernatant vaccine to determine whe ther active immune responses and protection could be induced in this age gr oup in the absence of maternal antibodies; All calves responded to vaccinat ion with high titers of IgM antibodies to capsular polysaccharide within 1 wk of primary vaccination. Mean titers of IgG1 and IgG2 antibodies to this antigen increased significantly by 2 wk after secondary vaccination, but pe ak antibody titers were low. All of the vaccinated calves seroconverted wit h production of leukotoxin-neutralizing antibodies, but peak antibody titer s were low. Vaccinated calves experienced considerable lung damage after ex perimental challenge, but survival rate, clinical scores, and percent lung involvement were significantly better than those of control (placebo-inject ed) calves.