Effects of L-carnitine on fetal growth and the IGF system in pigs

Fetuses were removed at mid-gestation from sows fed a common diet with a 50 g top dress of 0 (control, n = 6) or 100 mg L-carnitine (n = 6). Porcine embryonic myoblast (PEM) proliferation was evaluated at 36, 48, 60, and 72 h post-plating. Treatment did not affect (P > 0.05) number of cells/cm2, but number of cells/cm2 increased (P < 0.01) between each evaluation. Between 36 and 48 h, number of doublings was greater (P < 0.01) in L-carnitine cultures than controls. When PEM were incubated with L-carnitine (3.125, 6.25, 12.5, 25, 50, and 100 muM; n = 4) and compared to a control, no proliferation differences were detected (P > 0.05). At 96 h post-plating, no treatment difference (P > 0.05) for IGF-I or IGFBP-5 mRNA levels were found. However, PEM isolated from sows fed L-carnitine had decreased (P < 0.05) IGF-II, IGFBP-3, and myogenin (61, 59, 67%, respectively) mRNA levels compared to controls. A treatment x day interaction (P = 0.02) was observed for maternal circulating total carnitine. Sows fed L-carnitine had higher ( P < 0.05) concentrations of total carnitine at d 57 than controls. Supplementing sows L-carnitine resulted in larger (P = 0.02) litters (15.5 vs 10.8) that tended (P = 0.07) to be heavier (1,449.6 vs 989.4 g) without affecting fetal (P = 0.90) weights in comparison to controls. No treatment or side effect was detected ( P > 0.05) for muscle and liver IGF-I, IGF-II, and IGFBP-3 or muscle IGFBP-5 mRNA levels. A negative correlation (P < 0.05) between muscle IGF-I mRNA and fetal growth traits for L-carnitine, but no correlation (P > 0.05) for either treatment in hepatic tissue was observed. No treatment differences (P > 0.05) in uterine or placenta IGF-I, IGF-II, IGFBP-3, and IGFBP-5 mRNA levels were found. In placenta, IGF-I and IGF-II mRNA levels were higher (P < 0.05) on the left than the right side. Placenta expression of IGFBP-3 was not affected (P > 0.05) by side, but the left side had a tendency (P = 0.07) to have higher IGFBP-5 mRNA levels than the right. These findings suggest supplementing L-carnitine to gestating sows is beneficial for fetal growth and development.