Development of fiber type composition and fiber diameter in the longissimus muscle of the domestic pig (Sus scrofa domesticus)

: The development of fiber types composition and fiber diameter in porcine longissimus muscle from birth to the age of 5 years was examined by means of cross-sectional study. The fiber types were classified in the following manner: FTG = fast-twitch-glycolytic, FTO = fast-twitch-oxidative and STO = slow-twitch-oxidative. The percentage on the oxidative fibers decrease from 60.8% on the 1st d to 39.1% on the 100th d of life. On the 1800th d only 26.5% oxidative fibers are present. The average diameters of fiber types increase during the whole examination period, especially to the 100th d of life. The initial gradation of fiber diameter FTG = 63 micron, FTO = 62 micron, STO = 56 micron converts during growth into STO = 112 micron, FTO = 108 micron, FTG = 104 micron. A common representation of muscle fiber diameter growth curve and rump length growth curve demonstrates different growth modes of muscle and skeleton.