Abstract
Bovine respiratory disease (BRD) causes significant economic losses in dairy calves. The induction of an early immune response via parenteral vaccination is complicated by the interference of colostral immunity. In this study, we investigated early immunization against selected conserved bacterial antigens. Calves were vaccinated twice intranasally and then subcutaneously with Histophilus somni recombinant proteins (rOMP40, rHsp60) mixed with one of two adjuvants: CpG ODN2007 or MPLA. The control group (Con) was injected with PBS. The first immunization was done between 24–48 hours of life, and then twice in two weeks intervals. Blood, nasal, and saliva secretion samples were collected directly before vaccination (S1-S3), 42–44 (S4) and 59–61 day of life (S5). Antibodies (IgG1/IgG2/IgM/IgA in serum; IgG1/IgA in secretions) against both vaccine antigens were detected in all samples. Intranasal and subcutaneous vaccinations using the described compositions did not increase antibody reactivity against the tested proteins. The reactivity of serum IgG1, IgM, and IgA rOMP40 antibodies was significantly higher in S1 in all groups than that in the other samplings (p˂0.01). Significant differences in the reactivity of serum anti-rOMP40 antibodies between groups were identified in S1 (IgA reactivity was higher in the CpG vs. MPLA group; p < 0.05), S4 (IgM reactivity was higher in Con vs. CpG group; p < 0.05), and S5 (IgG1 reactivity was higher in the MPLA vs. Con group; p < 0.05). The lack of consistent changes in antibodies in subsequent samplings (S4 and S5) hinders the drawing of conclusions regarding the effect of immunization on antibody reactivity. In the future, different types of adjuvants should be considered to evaluate their usefulness in early immunization.