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We hypothesized that maternal nutrition and day of gestation would impact utero-placental mRNA expression of the nutrient transporters , , , , and in beef heifers. Crossbred Angus heifers (n = 49) were estrous synchronized, bred via AI, assigned to nutritional treatment (CON = 100% of NRC requirements for 0.45 kg/d gain and RES = 60% of CON) and ovariohysterectomized on d 16, 34, or 50 of gestation (n = 6 to 9/d); Non-bred, non-pregnant (NB-NP) controls were fed the CON diet, not bred, and were ovariohysterectomized on d 16 of the synchronized estrous cycle = 6). The resulting arrangement of treatments was a 2 × 3 factorial + 1 (CON vs. RES × d 16, 34, or 50 + NB-NP controls). Caruncle (CAR), intercaruncular endometrium (ICAR), and fetal membranes (FM [chorioallantois]), were obtained from the pregnant uterine horn (the uterine horn containing the conceptus) immediately after ovariohysterectomy. On d 50 cotyledons (COT), intercotyledonary placenta (ICOT) and amnion (AMN) were also collected. Relative expression of nutrient transporters was determined for each tissue utilizing NB-NP-CAR and NB-NP-ICAR tissues as the baseline. For FM, NB-NP endometrium served as the baseline. There was no interaction of day × treatment ( ≥ 0.20) for any genes in CAR. However, CAR expression of was greater ( < 0.01) on d 16 compared with d 34 and 50, and , , and were greater ( ≤ 0.05) on d 34 compared with d 16 and 50. In ICAR, was the only gene to be influenced by the day × treatment interaction ( = 0.01), being greater in d 50 CON compared with d 34 CON and d 16 and 50 RES. In ICAR, expression of was greater ( < 0.01) on d 16 compared with d 34, and expression of was greater ( < 0.01) on d 34 and 50 compared with d 16. In FM, expression of was greater ( = 0.04) on d 16 compared with d 50 of gestation, and expression of was greater ( < 0.01) on d 34 and 50 compared with d 16. On d 50, expression of , , and expression were all greater ( < 0.05) in AMN compared with COT and ICOT, and expression of was greater ( < 0.01) in ICOT compared with COT and AMN. These data indicate that day was a more influential factor for mRNA expression of utero-placental glucose and cationic AA transporters than maternal nutritional status in heifers during early pregnancy.

We hypothesized that both day of gestation and maternal nutrition would alter the relative mRNA expression of neutral and acid AA transporters , , , , and . Crossbred Angus heifers ( = 49) were synchronized, bred via AI, assigned to nutritional treatment (100% of NRC requirements for 0.45 kg/d gain [control heifers {CON}] and 60% of CON [restricted heifers {RES}]), and ovariohysterectomized on d 16, 34, or 50 of gestation ( = 6 to 9/d). Nonbred, nonpregnant (NB-NP) controls were ovariohysterectomized on d 16 of the estrous cycle ( = 6) after synchronization. The resulting arrangement was a 2 × 3 factorial + 1 (CON vs. RES × d 16, 34, or 50 + NB-NP controls). Tissues collected included caruncular endometrium (CAR), intercaruncular endometrium (ICAR), fetal membranes (FM; chorioallantois; d 16 and 34), cotyledonary placenta (COT; d 50 only), intercotyledonary placenta (ICOT; d 50 only), and amnion (AMN; d 50 only]). Relative expression of , , , , and was determined for each tissue using NB-NP CAR and NB-NP ICAR tissues for the baseline; for FM, endometrium from NB-NP controls served as the baseline. In CAR, no day × treatment interaction was observed ( > 0.05). However, day of gestation affected relative expression of , where expression on d 16 was greater ( < 0.01) than expression on d 34 and 50. Additionally, relative expression of and was greater ( ≤ 0.05) in pregnant heifers compared with NB-NP heifers. For ICAR, was influenced by a day × treatment interaction ( < 0.01), where expression in d 16 RES was greater ( ≤ 0.05) than that of any other day or nutritional treatment. Furthermore, expression in d 16 CON was greater ( ≤ 0.05) than that in d 50 RES, with those in d 34 CON and RES and d 50 CON being intermediate. In addition, was affected by day of gestation, where expression on d 16 was greater ( < 0.01) than that on d 34 and 50. A day × treatment interaction was not observed ( > 0.05) in FM; however, expression on d 34 was greater ( = 0.02) than on d 50, with that on d 16 being intermediate. Day of gestation also affected expression of , where expression on d 34 and 50 was greater ( < 0.01) than that on d 16. These data support our hypothesis in that both day of gestation and maternal nutrition affected the relative mRNA expression of AA transporter in ICAR, whereas day of gestation has a greater effect on the relative mRNA expression of other neutral and acidic AA transporters in the various tissues studied.