EFFECTS OF VARIOUS VACCINATION PROTOCOLS ON PASSIVE AND ACTIVE IMMUNITY TO PASTEURELLA-HAEMOLYTICA AND HAEMOPHILUS-SOMNUS IN BEEF-CALVES

Two field trials were conducted in a beef cow herd in Saskatchewan to determine the effectiveness of a combined Pasteurella haemolytica and Haemophilus somnus vaccine in increasing passively and actively acquir ed antibodies in beef calves. Vaccination of dams at 4 and/or 7 weeks prepartum was associated with increased antibody titers to P. haemolyt ica and H. somnus in their serum (P < 0.05), colostrum (P < 0.05), and serum of their calves at 3 days and 1 month of age (P < 0.05). There was no significant (P > 8.05) difference in antibody titers in the col ostrum and serum of calves from single or double vaccinated dams. Calv es vaccinated at 1 and 2 months of age in the face of maternal antibod ies to P. haemolytica and H. somnus had significantly (P < 0.05) highe r antibodies to P. haemolytica and H. somnus at 4 and 6 months of age than did unvaccinated calves. Calves vaccinated at 3 and 4 months of a ge in the face of low levels of preexisting antibodies had significant ly (P < 0.05) higher antibodies to P. haemolytica at 5 months of age a nd to H. somnus at 5 and 6 months of age than did unvaccinated calves. Calves vaccinated once at 4 months of age had significantly (P < 0.05 ) higher antibody titers to P. haemolytica and R. somnus at 4.5 months of age than did unvaccinated calves, but this difference was not appa rent at 6 months of age. These results suggest that vaccination of bee f cows with a combined Pasteurella haemolytica and Haemophilus somnus vaccine once at 4 weeks prepartum will significantly (P < 0.05) increa se passive antibody titers to P. haemolytica and H. somnus in their ca lves. Double vaccination of calves with preexisting maternal antibodie s at 1 and 2 months of age will increase antibody titers to P. haemoly tica and H. somnus until 6 months of age. Vaccination of beef calves w ith low levels of preexisting antibody at 3 and 4 months of age will i ncrease antibody titers to H. somnus until 6 months of age and to P. h aemolytica until 5 months of age. However, the level of antibodies ach ieved by vaccination may depend on the calves being studied, the level of preexisting antibodies, and the efficiency of passive transfer.