Bacterial isolates from tracheobronchial aspirates of healthy horses.

Of tracheobronchial aspirates from 50 clinically healthy Thoroughbred racehorses, 4 (8%) had aerobic bacteria with recognized pathogenicity, 12 (24%) contained transient bacterial isolates, and 37 (74%) had no bacterial growth. Of tracheobronchial aspirates from 36 pastured, nonracing racehorses, 3 (8%) had bacteria with recognized pathogenicity, 23 (64%) contained transient bacteria, and 10 (28%) had no bacterial growth. Anaerobes were not isolated from 12 of 12 pastured horses. Transient bacteria were isolated more often in the pastured horses.