Abstract
BACKGROUND: The efficacy of a single dose of an inactivated bovine respiratory syncytial virus (BRSV)--Parainfluenaza type 3 (PI3)--Mannheimia haemolytica (Mh) combination vaccine, in calves positive for maternal antibodies, was established in a BRSV infection study. RESULTS: As expected the single vaccination did not have any effect on the decline of BRSV-specific neutralising or ELISA antibody. The cellular immune system was however primed by the vaccination. In the vaccinated group virus excretion with nasal discharge was reduced, less virus could be re-isolated from lung tissues and the lungs were less affected. CONCLUSIONS: These results indicate that a single vaccination with an inactivated BRSV vaccine was able to break through the maternal immunity and induce partial protection in very young calves. It can be speculated that the level and duration of protection will improve after the second dose of vaccine is administered. A two-dose basic vaccination schedule is recommended under field conditions.