Maternal nutrition and stage of early pregnancy in beef heifers: Influence on glutamine transporter SLC38A7 in utero-placental tissues from d 16 to 50 of gestation

We hypothesized that maternal nutrition and day of gestation would influence the abundance of SLC38A7 in heifer utero-placental tissues. Angus-cross heifers (n = 49) were synchronized, bred via AI, assigned to nutritional treatment (CON = 100% of 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 (NB) controls were ovariohysterectomized on d 16 of the estrous cycle (n = 6). Uterine cross sections were taken from the horn ipsilateral to the CL, fixed in NBF, embedded, sectioned at 5 µm, and stained for SLC38A7. For each image, the areas of fetal membrane (FM; chorioallantois), endometrium (ENDO), superficial glands (SG), deep glands (DG), and myometrium (MYO) were included for further analyses. Analysis of FM was only conducted on d 34 and 50. Images were analyzed for relative intensity of fluorescence as an indicator of SLC38A7 abundance. Abundance of SLC38A7 was greater in NB vs. Pregnant heifers (d 16, 34, and 50) in ENDO, SG, and DG (P < 0.05). On d 16, SLC38A7 was greater in DG compared with ENDO and MYO (P < 0.0001). On d 34, SLC38A7 was greater in FM compared with DG and MYO (P < 0.0001). On d 50, SLC38A7 was greater in all tissues compared with MYO (P < 0.0001). Comparison of abundance across d 34 and 50 determined that SLC38A7 was greater in CON compared with RES heifers across both days and all tissues (P = 0.03). These data indicate that the abundance of SLC38A7 differs across uterine tissue types from d 16 to 50, and at least on d 34 and 50 supports our hypothesis that maternal nutrition during the first 50 days of gestation alters the abundance of SLC38A7 in bovine utero-placental tissues.