Effectiveness of an experimental subunit ovine <i>Mannheimia haemolytica</i> respiratory vaccine in reducing pneumonia in lambs.

Although vaccination with the experimental subunit <i>M. haemolytica</i> vaccine induced high LtxA and TbpB antibodies, it did not reduce clinical disease in lambs following an experimental challenge study or in a controlled randomized field trial in a commercial sheep operation. Further research is required to identify additional protective antigens for a safe and effective ovine respiratory vaccine to reduce pneumonia losses in commercial sheep flocks.