RESUMO
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.
Assuntos
Desenvolvimento Fetal/fisiologia , Desenvolvimento Muscular/fisiologia , Prenhez , Suínos/embriologia , Animais , Feminino , Idade Gestacional , Masculino , GravidezRESUMO
Ractopamine hydrochloride (RAC) improves swine production efficiency by redirecting nutrients to favor muscle accretion rather than fat deposition. In the present study, the time-dependent effect of RAC feeding on performance, plasma urea N (PUN) concentrations, and carcass traits of finishing pigs were evaluated. In a 28-d growth study, 80 barrows (average initial BW = 69.4 ± 7.9 kg) were assigned to 1 of 5 treatments in a randomized complete block design with 8 replicate pens per treatment and 2 pigs per pen. The pigs were fed a corn-soybean meal-based diet with no added RAC (control) or 10 mg of RAC/kg fed for 7, 14, 21, or 28 d before slaughter. All diets were formulated to contain 0.88% standardized ileal digestible Lys (1.0% total Lys) and 3.23 Mcal of ME/kg. Individual pig BW and pen feed disappearance were recorded weekly to determine BW changes, ADG, ADFI, and G:F. Anterior vena cava blood samples were taken on d 28 for determination of PUN concentrations. After 28 d on trial, the pigs were slaughtered and carcass measurements made at 24 h postmortem. Overall, providing pigs with different RAC feeding durations did not affect the final BW and ADFI but resulted in a tendency (P = 0.09) for a linear increase in ADG and a linear improvement (P = 0.003) in G:F. No effect of RAC feeding was found for weekly ADFI. Weekly improvements (P < 0.05) in ADG and G:F were observed over the first 21 d of RAC feeding. However, the growth response declined (P < 0.05) in wk 4 of RAC treatment. The concentrations of PUN exhibited a quadratic decrease (P = 0.004) as the RAC feeding duration increased. Although RAC feeding did not affect any backfat measurements and carcass length, increasing the RAC feeding duration linearly increased HCW (P = 0.01), dressing percentage (P = 0.03), LM depth (P = 0.001), LM area (P < 0.001), muscle-to-fat ratio (P = 0.004), and predicted carcass lean percentage (P = 0.02). These results indicate that a greater growth rate was achieved within the first 21 d of RAC feeding whereas the magnitude of carcass response was directly dependent on the duration of RAC feeding.