The influence of age on maternal inheritance of breast muscle morphology in turkeys1

Abstract

It was apparent in previous studies at our institution using turkeys that measurements of muscle fibers and extracellular spacing were not adequate to explain what was observed in entire pectoralis major muscle sections. A rating system was developed in which muscle sections were rated from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Maternal inheritance was observed at 16 wk of age but not at 8 or 20 wk of age. The purpose of the current study was to determine the effect of age on maternal inheritance. A line (F) selected long-term for increased 16-wk BW, its randombred control (RBC2), and reciprocal crosses between them were compared from 8 through 18 wk of age. Samples of pectoralis major muscle were obtained in a manner to avoid muscle contraction. After being fixed and cross-sectioned, the muscle samples were stained with hematoxylin and eosin and rated by 4 individuals. No significant difference among genetic groups was observed in scores at 8 wk of age. At 10 wk of age, the F line had lower scores than the other genetic groups. Maternal inheritance was suggested at 12 wk of age. The scores for RBC2 were higher than those for F, whereas the F x RBC2 cross did not differ from the pure RBC2 line score at this age. Although the RBC2 x F scores were higher than the pure F-line scores at 12 wk, they were lower than those of the F x RBC2 crosses. From 14 through 18 wk of age, the scores for the RBC2 line were higher than those for the F line and the maternal inheritance was absolute because the value for the individual crosses did not differ from that of the maternal parent. Based on the results, the type of mating used to produce commercial turkeys would have a major effect on breast muscle morphology from 12 through 18 wk of age.