Figure 5. Tonsils are a major site of M. bovis colonization in the upper respiratory tract.

At 14 days after oral inoculation of calves, mycoplasma numbers in nasal passages and tonsils were determined. Calves infected by oral ingestion of M. bovis had significantly higher (about 1 log higher) microbial loads in tonsils than did transtracheally-inoculated calves. Mycoplasmas were not recovered from any tissue of any control calf (N = 8). For visual purposes, tissues with identical scores have been shown with values slightly offset. Asterisks “*” denotes a significant difference between groups (P≤0.05).