分别饲喂100%(对照;CON;n=13)或70%(营养限制;NR;n=13)的可代谢能和可代谢蛋白质需求,怀孕,从妊娠到分娩的第160天。治疗前和妊娠181至265天每21d对子宫动脉进行多普勒超声检查。收集了被驱逐的胎盘,和同侧子叶组织取样以评估相对信使核糖核酸(mRNA)表达。胎盘分为同侧和对侧,解剖(子叶与间叶),干了。用营养平面分析数据,治疗开始日期,和小牛性别(当P<0.25时)为固定效应。子宫血流量包括日和营养平面×日作为重复测量。我们之前报道过产胎后,NR大坝重量比CON低64公斤,BCS低2.0公斤,但小腿出生体重没有受到影响。营养飞机开始后,NR大坝的母亲心率低于CON(P<0.001)。营养平面不影响(P≥0.20)子宫动脉血流动力学,但所有变量均受影响(P≤0.04)。与CON相比,NR大坝的对侧子叶和胎盘重量较少(P≤0.04),对侧子叶间重量和子叶数量较少(P≤0.10),但同侧和整个胎盘重量不受影响(P≥0.13)。NR大坝的同侧胎盘重量占胎盘总重量的百分比大于CON(P=0.03)。整个胎盘子叶:NR大坝的子叶间重量小于CON(P=0.01)。胎盘效率不受营养平面的影响(P=0.89)。与CON相比,NR大坝的GLUT3和SNAT2的子叶相对mRNA表达更高(P≤0.05),而GLUT1,GLUT4和NOS3的相对表达更高(P≤0.07)。营养平面不影响(P≥0.13)GLUT5、4F2hc的相对mRNA表达,CAT1,LAT1,LAT2,VEGFA,FLT1,KDR,GUCY1B3和PAG2。尽管对侧胎盘生长较少,经历妊娠晚期营养限制的牛肉母牛维持了子宫动脉血流和胎盘总质量,并在子叶中上调了4种营养转运蛋白和1种血管生成因子,所有这些都可能有助于保护胎儿的生长。
Fall-calving primiparous beef females [body weight (BW): 451 ± 28 (SD) kg; body condition score (BCS): 5.4 ± 0.7] were individually-fed either 100% (control; CON; n = 13) or 70% (nutrient restricted; NR; n = 13) of metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from day 160 of gestation to parturition. Doppler ultrasonography of both uterine arteries was conducted pre-treatment and every 21 d from days 181 to 265 of gestation. Expelled placentas were collected, and ipsilateral cotyledonary tissue was sampled to assess relative messenger ribonucleic acid (mRNA) expression. Placentas were separated into ipsilateral and contralateral sides, dissected (cotyledonary vs. intercotyledonary), and dried. Data were analyzed with nutritional plane, treatment initiation date, and calf sex (when P < 0.25) as fixed effects. Uterine blood flow included day and nutritional plane × day as repeated measures. We previously reported that post-calving, NR dams weighed 64 kg less and were 2.0 BCS lower than CON, but calf birth weight was not affected. Maternal heart rate was less (P < 0.001) for NR dams than CON after nutritional planes began. Nutritional plane did not affect (P ≥ 0.20) uterine artery hemodynamics, but all variables were affected (P ≤ 0.04) by day. Contralateral cotyledonary and placental weight were less (P ≤ 0.04) and contralateral intercotyledonary weight and number of cotyledons tended to be less (P ≤ 0.10) for NR dams than CON, but ipsilateral and whole placental weights were not affected (P ≥ 0.13). Ipsilateral placental weight as a percentage of total placental weight was greater (P = 0.03) for NR dams than CON. Whole placental cotyledonary: intercotyledonary weight was less (P = 0.01) for NR dams than CON. Placental efficiency was not affected (P = 0.89) by nutritional plane. Cotyledonary relative mRNA expression of GLUT3 and SNAT2 was greater (P ≤ 0.05) and relative expression of GLUT1, GLUT4, and NOS3 tended to be greater (P ≤ 0.07) for NR dams than CON. Nutritional plane did not affect (P ≥ 0.13) relative mRNA expression of GLUT5, 4F2hc, CAT1, LAT1, LAT2, VEGFA, FLT1, KDR, GUCY1B3, and PAG2. Despite less contralateral placental growth, beef heifers experiencing late gestational nutrient restriction maintained uterine artery blood flow and total placental mass and had 4 nutrient transporters and 1 angiogenic factor upregulated in cotyledons, all of which likely contributed to conserving fetal growth.
Nutrient requirements increase substantially during late gestation in the beef female to support fetal, uteroplacental, and mammary growth, and in the still-growing heifer, nutrients are also needed for maternal tissue growth. During pregnancy, the placenta serves as the interface for the metabolism and transport of nutrients, gases, and wastes between maternal and fetal circulations. Inadequate gestational nutrition can result in placental insufficiency and intrauterine growth restriction of the offspring, resulting in postnatal consequences. How late gestational undernutrition in beef heifers impacts the factors involved in placental nutrient transport capacity is poorly understood. We observed that late gestational nutrient restriction in heifers decreased maternal heart rate, but total uterine artery blood flow was not affected. Additionally, total placental mass was maintained, while cotyledonary expression of 4 nutrient transporters and an angiogenic factor were upregulated in placentas of nutrient restricted dams, which collectively allowed for similar calf birth weights as adequately-fed dams.