Lung growth of the turkey, Meleagris gallopavo: II. Comparison of two genetic lines.

Comparisons of lung growth in two genetic lines of turkeys, one unselected and one selected for increased body mass, were used to evaluate the lung's alteration in structure with changes in body form or physiology. Seventy-two male turkeys, 36 genetically selected for early rapid growth and large pectoral musculature, and 36 unselected birds, were killed at 12 different ages to compare lung growth in the two lines. Body weights and lung volumes were determined. A three-level cascade sampling system was used to prepare lung tissue for qualitative and quantitative observation by light microscopy. Allometric equations describing growth of lung volume and lung compartments relative to body weight in two phases (tissue proliferation and equilibrated growth) were compared between lines of turkey for differences in slopes or intercepts. Means of data for 112- and 420-day-old birds were also compared. There were no qualitative histological differences observed between lungs of the two lines of turkey, yet there were morphometric differences in lung growth relative to body weight. During equilibrated lung growth, there was less rapid growth of air and blood capillary volumes and surfaces relative to body weight in the selected than in the unselected turkey. The gas-exchange compartment did not enlarge concomitant with the large increase in muscle mass of the selected turkeys, while large-vessel volume and small-airway volume grew similarly to body weight in both turkey lines. We conclude that the lung of the selected line of turkeys did not show an enlarged gas-exchange compartment relative to the greater body muscle mass, but it did show enlarged vessels and conducting airways.