DEVELOPMENT OF THE THORACIC AIR SACS OF TURKEYS WITH AGE AND REARING CONDITIONS

Cytology and structure of the thoracic air sac of turkeys were investi gated at four different ages (26-day embryo, 1 day, 2 wk, and 10 wk ol d) and two rearing conditions (isolation and commercial). Cytology was performed by guided fiberoptic endoscopy on the left thoracic air sac of each bird. The right thoracic air sac was sampled for light and el ectron microscopy. Heterophils were the most common nonepithelial cell found in air sac fluid, followed by macrophages and lymphocytes. Macr ophages were most abundant in 1-day-old turkeys and turkeys raised in commercial conditions. The epithelium of the air sac consisted of squa mous and cuboidal cells, with a few ciliated columnar and nonciliated columnar cells. Cuboidal cells had similar characteristics to type II pneumocytes. The mucociliary system was organized in tracts extended f rom the ostium to the posterior parts of the air sac. The number of ci liated tracts decreased with age, and the air sacs of commercial turke ys had a larger proportion of ciliated epithelium than did those of is olation birds. The epithelium may protect against disease by a structu red mucociliary transport system, the production of surfactant, and ph agocytosis of foreign particles. Differences in cytology and structure may reflect the maturation of the immune system and/or response to en vironment.