The effects of nutritional restriction on endogenous retroviruses and placentation during the first 50 d of gestation in beef heifers

Abstract Text:

The objectives of this study were to evaluate the effects of maternal nutrient restriction and day of gestation on mRNA expression of syncytin-Rum1, bovine endogenous retrovirus K1 (BERV-K1), interferon-tau (INF-τ), and pregnancy specific protein B (PSP-B). At breeding (0 d), crossbred heifers (n = 49; ~15 mo of age; initial BW = 324.9 kg) were assigned to dietary treatments, control (fed to gain 0.45 kg/d BW gain) or restricted (60% of control). Heifers were ovariohysterectomized at d 16, 34, or 50 resulting in a 2 × 3 factorial. Non-bred, non-pregnant heifers (n = 6; NP), on the control diet, were ovariohysterectomized as baseline controls on d 16 of the estrous cycle. The tissues collected consisted of pregnant horn caruncle (P-CAR), pregnant horn inter-caruncle (P-ICAR), non-pregnant horn caruncle (NP-CAR), non-pregnant horn inter-caruncle (NP-ICAR), and fetal membrane (chorioallantoic; FM). Relative gene expression was calculated using the delta delta Ct method with β-actin as the reference gene and NP as the control tissue. Data were analyzed using PROC GLM of SAS with the model including d of gestation, nutritional treatment, and their interaction. There was significant d of gestation × nutrition interaction for expression of BERV-K1 in NP-CAR and INF-τ in FM while all other interactions were not significant (P > 0.08). Expression of INF-τ was influenced by d of gestation and nutritional treatment in FM, with d 16 restricted being greatest (5,781 fold; P < 0.01) followed by d 16 control FM (3,324 fold); the remaining d and treatments were not different. In FM, BERV-K1 was greatest (P < 0.01) on d 34 (2,961 fold) compared with d 16 and 50 (5 and 1,861 fold, respectively). Syncytin-Rum1 increased (P = 0.04) in FM throughout the first 50 d (375 fold) of gestation. Syncytin-Rum1 expression in P-ICAR was greatest (P = 0.01) at d 16; however, syncytin-Rum1 expression in P-CAR tended (P = 0.09) to be greater at d 50. Expression of PSP-B increased (P < 0.01) throughout early gestation until d 50 in both NP-CAR (316 fold) and P-CAR (18,215 fold). Although nutritional restriction did not influence endogenous retrovirus expression in maternal or fetal tissues, it did influence INF-τ expression. These data suggest that both BERV-K1 and syncytin-Rum1 may interact with PSP-B during the establishment of the fetomaternal interface and syncytial plaques. 

Keywords: beef heifers, early gestation, endogenous retroviruses, nutrient restriction