Inheritance of breast muscle morphology in turkeys at sixteen weeks of age

The inheritance of morphology of the pectoralis major muscle in turkeys at 16 wk of age was studied in a randombred control line (RBC2), a subline (F) of RBC2 selected long term for increased 16 wk BW only, and F1 and F2 crosses of the F and RBC2 lines. Samples of pectoralis major muscle were obtained from 10 males and 10 females of each genetic group in a manner to avoid muscle contraction. After being fixed and cross sectioned, the muscle samples were stained with hematoxylin and eosin to view muscle morphology. The stained sections were analyzed for muscle fiber width, number of fibers in a 136-micrometer2 area, and extracellular matrix perimysial (PW) and endomysial (EW) width in areas of sections in which accurate measurements could be made. Because muscle damage was evident in some sections and, therefore, morphological measurements might not have provided a complete overview of muscle morphology, sections of the F2 crosses were subjectively rated by 4 people. The ratings ranged from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Ratings of 2 to 4 were intermediate to these extremes. Creatine kinase concentrations of blood samples taken immediately prior to collecting muscle tissue were obtained and correlated with muscle section ratings within genetic group and sex. The F and RBC2 lines differed in PW and EW but not in individual fiber measurements. In the F1 generation, heterosis was -10.4% ( P is less than or equal to 0.01), 19.7% ( P is less than or equal to 0.05), -25.2% P is less than or equal to 0.01), and -34.3% (P is less than or equal to 0.01), respectively, for fiber width, number of muscle fibers, PW, and EW. The F2 crosses differed only in EW based on measurements of sections in which accurate measurements could be made. However, based on subjective ratings of the muscle sections, possible maternal inheritance was suggested, as the orthogonal contrast was significant (P is less than or equal to 0.01) for crosses with F dams as F1 parents vs. those with RBC2 dams as F1 parents, confirming a previous study. The correlation coefficient between creatine kinase concentration and muscle section ratings was -0.282 (P is less than or equal to 0.01) after adjustment for line and sex effects.