Ovine pneumonia is an economic important disease and there is currently no commercial vaccine available in New Zealand. Bovilis MH is a registered bovine respiratory vaccine based on serotype A1 Mannheimia haemolytica and its leukotoxin. In this study, we investigated the protective effect of the vaccine in lambs against a challenge with a serotype A2 M. haemolytica. Colostrum-deprived lambs were recruited into a vaccine (n=12) or placebo (n=12) group. At 4-5 weeks of age, lambs in the vaccine group were injected subcutaneously with 1 ml Bovilis MH vaccine, and revaccinated 4 weeks later, while the placebo group received 1 ml saline at each occasion. Two weeks after the revaccination, all lambs were challenged intratracheally with parainfluenza virus 3, and with A2 M. haemolytica at day 7 post-viral challenge. After the M. haemolytica challenge, pyrexia and dyspnoea occurred on fewer occasions in the vaccine group compared to the placebo group, but not significantly (p = 0.10). The average lung consolidation percentage for the vaccine and placebo groups were 18.9% and 38.8%, respectively (p = 0.181). The vaccine group had a significantly lower lung/bodyweight percentage than the placebo group (1.45 ± 0.29 vs 2.04 ± 0.94, p = 0.047), suggesting the vaccine group had significantly less inflamed lungs than that in the placebo group. The vaccine group had significantly higher antibody titres 2 weeks post revaccination to antigens of M. haemolytica and leukotoxin from A1 and A2 serotypes than that for the placebo group (p < 0.05). The results suggested that the Bovilis MH vaccine provided partial protection against pneumonia in lambs induced by a heterologous serotype of M. haemolytica. The protective efficacy of Bovilis MH against ovine pneumonia now requires to be tested in the field situation.