Study on the Effect of N-Carbamylglutamate (NCG) on Reproductive Performance and Regulation Mechanism of Primary Lake Sheep

The aim of this study was to investigate the effects of dietary supplementation with 0.11% N-carbamylglutamate (NCG) during early pregnancy (0–90 days) on reproductive performance and fetal development, and to elucidate the underlying placental regulatory mechanisms in primiparous Hu sheep. Twenty-two 10-month-old sexually mature primiparous Hu sheep meeting the mating criteria were randomly assigned to two groups. The control group was fed a basal diet, while the NCG group received the basal diet supplemented with 0.11% NCG, with both feeding regimens maintained for 90 days. By measuring uterine and fetal growth indices, maternal plasma biochemical parameters, and amino acid levels, as well as assessing cotyledon indices and observing cotyledon morphology and histological structure, basic data related to placental function and fetal growth in pregnant ewes was collected. Combined with transcriptomic sequencing of maternal placental tissue, the mechanism by which NCG influences placental function and fetal growth and development in pregnant ewes was further investigated. The supplementation of NCG could increase the number of fetuses, total weight of fetuses, the number of corpus luteum and the ratio of fetuses to corpus luteum, but the difference was not significant (p > 0.05). The levels of plasma NO, inducible Nitric Oxide Synthase (iNOS) and several amino acids were significantly increased (p < 0.05). In ewes’ uteri, the average uterine weight, number of uterine glands, total cotyledon weight, and average weight per cotyledon were significantly increased (p < 0.05), whereas uterine mucosal thickness was markedly decreased. The Quantitative Real-time PCR (q-PCR) results for differentially expressed genes were consistent with those of transcriptomic analysis, showing significant changes in the expression levels of certain differentially expressed genes in maternal placental tissues. These changes regulated pathways such as vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF), phosphatidylinositol 3-kinase–protein kinase B (PI3K–AKT) signaling pathways and Mitogen-Activated Protein Kinase (MAPK) pathway, which are involved in angiogenesis, energy supply and metabolism, and somatic growth and development. Dietary supplementation with NCG during early pregnancy can significantly improve the reproductive performance of primiparous Hu sheep, optimize the intrauterine environment and nutrient supply, and thereby facilitate pregnancy maintenance and fetal development. The underlying mechanism may involve promoting endogenous arginine synthesis in ewes, increasing plasma levels of NO, arginine, and certain amino acids, which collectively validate the positive effects of NCG on the reproductive performance and growth of Hu sheep during early pregnancy at the molecular level.