Swine foetal myogenesis in different gestation periods.

This experiment was conducted to evaluate the effects of sex and uterus position on swine foetal myogenesis at different gestational ages. Fifteen primiparous sows were divided into three groups according to gestational age: 50, 80, and 106 days. The experiment was a block randomized factorial design with two sexes (male and female) and three uterine regions (apex, middle, and base). After slaughter, each uterus horn was divided into three segments of equal length: apex region near the ovary; base region near the uterine body; and the middle region, lying between the apex and base regions. The foetuses were weighed, identified, and longitudinally opened to harvest the semitendinosus muscle for later morphological analysis. After 50 days of pregnancy, male foetuses had greater (p < .05) weight than females. The number of primary fibres at 50 days of gestation was negatively correlated (r = -.29, p = .04) with the number of foetuses in utero. After 80 days, foetuses in the base region had less (p < .05) secondary area of muscle fibres compared to the apex region, which was accompanied by differences in the weight of the foetuses, the lowest weight were for foetuses located in the base region (p < .05). In the same period, the ratio of secondary to primary fibres had a positive correlation with weight. In conclusion, sex did not influence myogenesis in the gestational ages studied and the development of secondary muscle fibres of the foetuses at 80 days of gestation was affected by their uterine position with foetuses at the base of the uterine horn being less developed.