The effects of placental amino acid transporter gene expression and lamb development in primiparous versus multiparous Awassi ewes.

Optimal fetal growth in small ruminants fundamentally depends on the active transport of nutrients across the maternal-fetal interface. Although macroscopic variations in placental dynamics are known, the molecular mechanisms linking maternal reproductive status to placental nutrient transport pathways remain poorly defined. This study examined the influence of maternal parity on lamb birth metrics, neonatal morphological traits, serum amino acid concentrations, and the relative expression profiles of amino acid transporter genes in the cotyledons of indigenous Awassi sheep. Forty-two pregnant Awassi ewes were assigned to two experimental groups: mature young adult primiparous (n = 21; 20.4 ± 0.8 months of age; 1st gestation) and multiparous (n = 21; 38.2 ± 1.2 months of age; 2nd or 3rd gestation). Following natural singleton deliveries, phenotypic measurements and blood samples were collected from a representative cohort of ewes and their offspring (n = 14 pairs per parity). Total hydrolyzed serum amino acid profiles were quantified using gas chromatography-mass spectrometry. Relative mRNA expression levels of five specialized transporter genes in harvested cotyledon tissues were evaluated by quantitative real-time PCR. Lambs born to multiparous ewes had higher birth weights, wither heights, and body circumferences than those born to primiparous ewes (p < 0.05). Fold change in the expression of all target genes (SLC1A5, SLC7A8, SLC38A6, SLC3A1, and SLC7A5) in the cotyledonary tissues of multiparous ewes was increased (p < 0.05). Multiparous lambs had higher circulating concentrations of alanine, leucine, glycine, phenylalanine, histidine, lysine, and tyrosine, resulting in a higher total systemic amino acid concentration (p = 0.001). In contrast, primiparous lambs had higher concentrations of aspartic acid and glutamic acid (p < 0.05). In conclusion, parity-dependent regulation of cotyledonary amino acid transporters is a primary driver of prenatal resource allocation. Mature multiparous ewes upregulate essential transport machinery to clear nutrients from maternal circulation and concentrate them within the fetus, optimizing neonatal growth and structural development.