High prolificacy of sows and increased fetal survival lead to greater incidence of intrauterine crowding (IUC), which may then affect pre- and postnatal development of the progeny. The aim of the study was to assess the impact of IUC, using unilaterally hysterectomized- ovariectomized gilts (UHO), on organ and muscle development of their progeny at birth. In the study, 7 UHO and 7 intact control (Con) Swiss Large White gilts were used. At farrowing, if available, 3 male and 3 female progeny with a low (>0.8 and <1.2 kg), medium (>1.2 and <1.4 kg), and high (>1.6 kg) birth weight (BtW) were killed. Internal organs and brain were weighed, and semitendinosus (STN), psoas major (PM), and rhomboideus (RH) muscles were collected. Histological analyses were performed in PM, RH, and STN (dark and light portion) using myofibrillar ATPase staining after preincubation at pH 10.3. Myosin heavy chain (MyHC) polymorphism was determined in the PM using SDS-PAGE gel electrophoresis. Despite that only one-half of the uterine space was available, litter size was smaller only by 35% inUHO compared with Con gilts. However, UHO progeny tended to be lighter than Con progeny. Theaverage BtW of the selected piglets did not differ between the 2 sow groups, whereas PM and kidneys tended to be lighter in UHO than in Con progeny. Compared with Con progeny, the PM and the STNdark of UHO progeny had fewer secondary and total myofibers as well as fewer primary myofibers in the PM. In the RH, the secondary-to-primary myofiber ratio was smaller in UHO than in Con progeny, whereas the total number of myofibers did not differ. The relative abundance of fetal MyHC was less and that of type I MyHC tended to be greater in UHO than in Con offspring. With increasing BtW, organ and brain weights increased. Muscle cross-sectional area and total number of myofibers in the light portion of the STN were greater in high and medium than in low piglets. In conclusion, IUC reduced hyperplasia of secondary and total myofibers in the STNdark and PM. These effects were independent of the BtW and sex.

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