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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 Gennan 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. [ABSTRACT FROM AUTHOR]

Birth weight differences have been shown to affect body composition in pigs and other species. However, data on effects of birth weight differences on morphological and cellular traits of carcass in bulls with a longer fattening period are scarce. Consequently, we have analyzed 2 groups of bulls from an experimental F2 cross (Charolais × Holstein) with low birth weight (LBW; 35.6 ± 0.7 kg; n = 20) and high birth weight (HBW; 59.4 ± 0.9 kg; n = 20). All animals were kept in a tight stall barn from d 121; were fed a standardized, concentrate-based diet ad libitum; and were slaughtered at an age of 547 d. The feed intake was higher in the HBW group but feed conversion ratio was not different. Live weights were not different between the 4th and 15th month of age but then diverged, resulting in significantly higher weights at slaughter at 18 mo in the HBW group (717 ± 13 vs. 661 ± 10 kg; P < 0.05). Bulls of the HBW group accreted more protein (14.9 ± 0.15 vs. 14.4 ± 0.17%; P = 0.017) and LBW bulls accreted more fat (17.2 ± 0.81 vs. 14.3 ± 0.79%; P = 0.016) in the carcass. The absolute and relative weights of omental, perirenal, and visceral adipose depots were significantly higher in LBW bulls. Weight of longissimus (MLD) was higher in the HBW bulls (8.6 ± 0.15 vs. 7.7 ± 0.13 kg; P < 0.001) compared with LBW animals. However, there were no significant differences in muscle fiber traits in MLD. The intramuscular fat (IMF) content of MLD from LBW bulls was significantly increased compared with that of HBW animals (3.9 ± 0.5 vs. 2.5 ± 0.3%; P = 0.012). Analysis of cellular parameters of the IMF revealed increased diameters (94.4 ± 1.7 vs. 81.4 ± 2.4 μm; P < 0.01) of adipocytes and larger but not more marbling flecks as cause for higher IMF in LBW bulls. Our results demonstrate long-lasting effects of large differences in birth weight on carcass traits. Crossbred bulls could not compensate low birth weights even under ad libitum feeding regimen within a period of 18 mo in this experiment. Our data indicate that metabolic differences resulted in different partitioning of nutrients with a shift to lipid accumulation in bulls with lower birth weight in this crossbreed population. [ABSTRACT FROM AUTHOR]

Focuses on the chromosomal localization and partial cDNA sequence of the porcine adenocine triphosphate synthase subunit e gene. Origin of the clone; Comparison with related sequences; Chromosomal location.