This study was conducted to test the hypothesis that dietary supplementation with L-arginine during early pregnancy will ameliorate embryonic loss in pigs. Gilts were bred at the second estrus, and housed individually in pens and fed twice daily 1 kg of a corn- and soybean meal-based diet supplemented with 0.0%, 0.4%, or 0.8% L-arginine (w/w) between d 0 and 25 of gestation (Experiment 1) or between d 14 and 25 of gestation (Experiments 2 and 3). At d 25 (Experiment 1 and 2) or d 60 (Experiment 3) of gestation, gilts were hysterectomized to obtain uteri and conceptuses. Total RNA and protein were extracted from the frozen tissues. Quantitative RT-PCR, western blotting, and microarray analyses were performed to determine the changes of gene expression at mRNA and protein levels. Dietary supplementation with 0.8% L-arginine between d 0 and 25 of gestation decreased uterine weight, total number of fetuses, number of corpora lutea (CL), total fetal weight, total volume of allantoic and amniotic fluids, concentrations of progesterone in maternal plasma and allantoic fluid, compared to the control group. However, dietary supplementation with 0.4% or 0.8% L-arginine between d 14 and 25 of gestation increased total volume of amniotic fluid, total amounts of arginine in allantoic and amniotic fluids, total amounts of fructose and most amino acids in amniotic fluid, placental growth, and the number of viable fetuses per litter by 2. Dietary supplementation with 0.4% or 0.8% L-arginine between d 14 and 25 of gestation increased the total number of fetuses and number of live fetuses, rate of embryonic survival, and volumes of allantoic and amniotic fluids in gilts with 15 to 18 CL on d 60 of gestation compared with the control group. The abundance of placental protein and expression of mRNA related to the genes for arginine transport and metabolism, including cationic amino acid transporter 1, endothelial nitric oxide synthase (NOS3), phosphorylated-NOS3, ornithine decarboxylase, and guanosine triphosphate cyclohydrolase-I was increased by dietary supplementation with 0.8% L-arginine between d 0 and 25 of gestation. The abundance of total and phosphorylated mechanistic target of rapamycin was also enhanced by dietary 0.8% L-arginine supplementation between d 0 and 25 of gestation. Microarray analysis revealed that supplementation with 0.8% arginine between d 14 and 25 of gestation affected placental expression of 575 genes. Findings from the current study not only advance basic knowledge of mammalian reproductive biology, but also have important implications for developing practical means to enhance fertility in female pigs.

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