Effect of genetic increases in egg production, age, and sex on muscle development in turkeys

Breast muscle morphology was studied at 8 and 16 wk of age in a line (E) selected over 44 generations for increased egg production and its randombred control line (RBC1). A sample of 20 birds per sex-line-age subgroup was killed with restraint to prevent flapping of the wings. The skin was removed from the breast region, and a sample of breast muscle was obtained in a manner to prevent contraction. The muscle samples were dehydrated, cleared, embedded in paraffin, sectioned, and incubated and rehydrated prior to staining with hematoxylin and eosin. Four sections from the same muscle from each bird were placed on a slide, and the slides were viewed for muscle morphological characteristics with a microscope and digitally recorded. Five fields of each section were viewed. Representative sections for each bird were given a score by 4 individuals based on breast muscle morphology. The scores ranged from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Scores from 2 to 4 were intermediate to these extremes. Breast muscle morphology scores did not differ between lines or ages but there was a significant interaction between lines and ages. The scores increased in the RBC1 line from 8 to 16 wk of age, but the reverse was true for the E line. Scores were higher in males than females. The results of the present study suggest that selection for increased egg production in dam lines should not greatly influence breast muscle morphology in commercial turkeys.