Muscle fiber development during gestation determines the muscle structure at birth and establishes the conditions for muscle development in growing cattle. Differences in muscle structure among beef cattle breeds and between beef and dairy cattle are obvious already shortly after birth. The objective of the study was to investigate the development of muscle fibers and muscle fiber bundle structure in semitendinosus muscle of divergent cattle breeds from 3 mo of gestation until birth. Fetuses of German Angus (GA), Galloway (GW), Belgian Blue (BB), and Holstein Friesian (HF) were harvested at 3, 4.5, 6, or 9 mo of gestation. Muscle sections were analyzed for fiber size and types as well as for bundle structure. The results confirmed that primary muscle fiber development occurs mainly during the first trimester of gestation. All fibers were initially positive for fetal fast myosin. Slow myosin as a marker for fiber maturation was detected in primary fibers at 3 mo of gestation showing a weak immunostaining. During the second trimester, the intensity of immunostaining strongly increased indicating increased slow myosin protein expression. Concurrently, the shape of primary fibers changed from myotubes to myofibers whereas the size stayed nearly constant. The main increase in muscle mass during the second trimester was caused by secondary fiber development. As an example, the ratio between secondary and primary fibers increased in Holstein Friesian fetuses from 5.9 at 4.5 mo of gestation to 21.6 at 6 mo of gestation. Primary and secondary fibers continued to growth during the third trimester. Regional differences in the density of slow muscle fibers were detected leading to greater variation within the muscle than among breeds. Structural organization of muscle fibers in muscle fiber bundles developed early in fetal life. At first, large main bundles were visible. Smaller structural units defined as primary bundles were measurable at 6 mo of gestation when most fibers were developed. The size of primary bundles nearly doubled from 6 mo of gestation to birth in all breeds. In summary, differences among breeds in the early fetal muscle fiber development were detected in contractile differentiation and partly in muscle fiber bundle structure. A prolonged secondary fiber generation and altered contractile differentiation may be involved in breed differences of postnatal muscle development.
Muscle fiber development during gestation determines the muscle structure at birth and establishes the conditions for muscle development in growing cattle. Differences in muscle structure among beef cattle breeds and between beef and dairy cattle are obvious already shortly after birth.การวิจัยครั้งนี้มีวัตถุประสงค์เพื่อศึกษาการพัฒนาของเส้นใยกล้ามเนื้อและโครงสร้างเส้นใยกล้ามเนื้อมัดกล้ามเนื้อของโคพันธุ์ลูกผสมและกระบือปลักที่แตกต่างกันจาก 3 โมของการตั้งครรภ์ จนกระทั่งคลอด สายของเยอรมันแองกัส ( GA ) , กัลโลเวย์ ( GW ) เบลเยียมสีน้ำเงิน ( BB ) และโฮลสไตน์ฟรีเซี่ยน ( HF ) ที่อายุ 3 , 4 , 6 หรือ 9 โมของทารก Muscle sections were analyzed for fiber size and types as well as for bundle structure. The results confirmed that primary muscle fiber development occurs mainly during the first trimester of gestation. All fibers were initially positive for fetal fast myosin. Slow myosin as a marker for fiber maturation was detected in primary fibers at 3 mo of gestation showing a weak immunostaining. During the second trimester, the intensity of immunostaining strongly increased indicating increased slow myosin protein expression. Concurrently, the shape of primary fibers changed from myotubes to myofibers whereas the size stayed nearly constant. The main increase in muscle mass during the second trimester was caused by secondary fiber development. As an example, the ratio between secondary and primary fibers increased in Holstein Friesian fetuses from 5.9 at 4.5 mo of gestation to 21.6 at 6 mo of gestation. Primary and secondary fibers continued to growth during the third trimester. Regional differences in the density of slow muscle fibers were detected leading to greater variation within the muscle than among breeds.โครงสร้างของเส้นใยกล้ามเนื้อในเส้นใยกล้ามเนื้อมัดที่พัฒนาในช่วงต้นชีวิตทารก ตอนแรกกลุ่มหลักใหญ่คือมองเห็นได้ โครงสร้างหน่วยเล็ก เช่นการรวมกลุ่มหลักเป็นวัดที่ 6 โมของการตั้งครรภ์เมื่อเส้นใยมากที่สุด คือ การพัฒนา ขนาดของมัดหลักเกือบสองเท่าจาก 6 โมในครรภ์จะเกิดในทุกสายพันธุ์ กล่าวโดยสรุปความแตกต่างระหว่างพันธุ์ในช่วงต้นของการพัฒนาพบว่าเส้นใยกล้ามเนื้อหดตัวการหาอนุพันธ์และส่วนหนึ่งในโครงสร้างเส้นใยกล้ามเนื้อมัด รุ่นรองไฟเบอร์นานและเปลี่ยนแปลงที่แตกต่างอาจจะเกี่ยวข้องกับความแตกต่างของสายพันธุ์ การพัฒนากล้ามเนื้อหลัง .
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