Introduction - Bibersteinia trehalosi has been associated with respiratory disease in ruminants particularly in wild and domestic sheep. Recently, there has been an increased interest in B. trehalosi isolates obtained from diagnostic samples from bovine respiratory disease cases. This study evaluated the role of B. trehalosi in the bovine respiratory disease complex using an intra-tracheal inoculation model in calves. This study also evaluated the potential of haptoglobin-matrix metalloproteinase 9 (Hp-MMP 9) serum concentrations as a useful diagnostic tool in calves affected with B. trehalosi and M. haemolytica associated respiratory disease.

Materials and Methods - Thirty-five cross-bred dairy steers were inoculated intra-tracheally with either leukotoxin negative or leukotoxin positive B. trehalosi, Mannheimia haemolytica, a combination of leukotoxin negative B. trehalosi and M. haemolytica, or negative control. Physical examinations were conducted and serum samples were collected throughout the study. Calves were euthanized and necropsies performed on day 10 of the study.

Results - No significant differences were found between the groups of calves challenged with B. trehalosi alone or in conjunction with M. haemolytica and the negative control calves with respect to percent lung involvement, rectal temperature, respiratory or depression score, or serum Hp or Hp-MMP 9 concentration in this study. M. haemolytica inoculated calves, but not B. trehalosi inoculated calves had increased lung involvement compared to control calves. B. trehalosi was only cultured once from the lungs of inoculated calves at necropsy. Increases in serum Hp and Hp-MMP 9 concentrations for the M. haemolytica group became significantly different from other groups on day 7. The leukotoxin positive B. trehalosi group demonstrated increased serum Hp-MMP 9 concentrations on days 3-10 compared to pre-inoculation concentrations.

Conclusions - Based on these findings B. trehalosi may not be a primary pathogen of respiratory disease in cattle. Culture of B. trehalosi from diagnostic submissions should not be immediately identified as a primary cause of respiratory disease. Serum Hp-MMP 9 concentration is a useful diagnostic tool for detecting early pulmonary inflammation in calves challenged with B. trehalosi and M. haemolytica. Serum Hp-MMP 9 may also be a useful tool in detecting subclinical pulmonary inflammation in challenged calves.