Development of the thoracic air sacs of turkeys with age and rearing conditions.

Cytology and structure of the thoracic air sac of turkeys were investigated at four different ages (26-day embryo, 1 day, 2 wk, and 10 wk old) 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 electron microscopy. Heterophils were the most common nonepithelial cell found in air sac fluid. followed by macrophages and lymphocytes. Macrophages were most abundant in 1-day-old turkeys and turkeys raised in commercial conditions. The epithelium of the air sac consisted of squamous 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 from the ostium to the posterior parts of the air sac. The number of ciliated tracts decreased with age, and the air sacs of commercial turkeys had a larger proportion of ciliated epithelium than did those of isolation birds. The epithelium may protect against disease by a structured mucociliary transport system, the production of surfactant, and phagocytosis of foreign particles. Differences in cytology and structure may reflect the maturation of the immune system and/or response to environment.