Redifer Colby A, Rathert-Williams Abigail R, Meyer Allison M
Division of Animal Sciences, University of Missouri, Columbia, MO 65211, USA.
J Anim Sci. 2025 Jan 4;103. doi: 10.1093/jas/skaf163.
To investigate impacts of late gestational nutrient restriction in first-parity beef females on prenatal nutrient availability to calves, fall-calving heifers [body weight (BW): 472 ± 33 (SD) kg; body condition score (BCS): 5.4 ± 0.5] were individually-fed 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 calving. Maternal measures were determined every 21 d (BW and metabolites) or 42 d (BCS, backfat, and longissimus muscle area) during gestation and post-calving. Doppler ultrasonography of both uterine arteries was conducted every 21 d until day 244 of gestation. At birth, calf BW and size were measured, and expelled placentas were dissected and dried. Targeted messenger ribonucleic acid (mRNA) expression was determined for cotyledons. Data were analyzed with nutritional plane, treatment initiation date, heifer's sire, and calf sex (when P < 0.25) as fixed effects. Metabolites and uterine blood flow included day and nutritional plane × day as repeated measures. Circulating glucose was less (P = 0.05) for NR dams than CON. Circulating urea N and triglycerides were less (P ≤ 0.05), but non-esterified fatty acids were greater (P ≤ 0.05), for NR at most timepoints after treatment initiation. Post-calving, NR dams were 62.1 kg and 2.1 BCS less (P < 0.01) than CON. Moreover, NR had less (P < 0.01) backfat and longissimus muscle area, but similar (P = 0.72) shoulder height compared with CON. Heart rate was less (P < 0.01) for NR dams than CON after treatment initiation. Nutritional plane did not affect (P ≥ 0.15) ipsilateral, contralateral, or total uterine artery blood flow. Number of cotyledons was greater (P = 0.03), average cotyledon weight was less (P = 0.04), and total placental weight tended to be less (P = 0.10) for NR than CON. Cotyledonary relative mRNA expression of GLUT1 was greater (P = 0.04) and SNAT2 tended to be greater (P = 0.07) for NR, but other nutrient transporters, angiogenic factors, and PAG2 were not affected (P ≥ 0.13). Calves born to NR dams weighed 14.4% (P = 0.03) less at birth and had smaller (P ≤ 0.03) heart girth and volume than CON. Despite catabolizing maternal tissue stores, beef heifers experiencing late gestational nutrient restriction had altered circulating metabolites and smaller placentas, independent of a reduction in uterine blood flow, which compromised fetal growth.
为研究头胎肉牛妊娠后期营养限制对胎儿产前营养供应的影响，对秋季产犊的小母牛[体重（BW）：472±33（标准差）千克；体况评分（BCS）：5.4±0.5]从妊娠第160天至产犊期间分别饲喂维持、妊娠和生长所需代谢能和代谢蛋白的100%（对照组；CON；n = 13）或70%（营养限制组；NR；n = 13）。在妊娠期间和产后，每21天（测量BW和代谢物）或42天（测量BCS、背膘和背最长肌面积）测定母体指标。在妊娠第244天前，每21天对双侧子宫动脉进行一次多普勒超声检查。出生时，测量犊牛的BW和大小，并对排出的胎盘进行解剖和干燥处理。测定子叶中靶向信使核糖核酸（mRNA）的表达。以营养水平、处理起始日期、小母牛的父亲和犊牛性别（当P<0.25时）作为固定效应分析数据。代谢物和子宫血流数据包括天数以及营养水平×天数作为重复测量因素。NR组母羊的循环葡萄糖水平低于CON组（P = 0.05）。处理开始后，在大多数时间点，NR组的循环尿素氮和甘油三酯水平较低（P≤0.05），但非酯化脂肪酸水平较高（P≤0.05）。产后，NR组母羊的体重比CON组轻62.1千克，BCS低2.1（P<0.01）。此外，与CON组相比，NR组的背膘和背最长肌面积较小（P<0.01），但肩高相似（P = 0.72）。处理开始后，NR组母羊的心率低于CON组（P<0.01）。营养水平对同侧、对侧或总子宫动脉血流无影响（P≥0.15）。NR组的子叶数量较多（P = 0.03），平均子叶重量较轻（P = 0.04），总胎盘重量有较轻的趋势（P = 0.10）。NR组子叶中葡萄糖转运蛋白1（GLUT1）的相对mRNA表达较高（P = 0.04），钠依赖性中性氨基酸转运蛋白2（SNAT2）有较高的趋势（P = 0.07），但其他营养转运蛋白、血管生成因子和妊娠相关糖蛋白2（PAG2）不受影响（P≥0.13）。NR组母羊所生犊牛出生时体重比CON组轻14.4%（P = 0.03），胸围和体积也较小（P≤0.03）。尽管分解母体组织储备，但妊娠后期经历营养限制的肉牛小母牛循环代谢物发生改变，胎盘较小，且与子宫血流量减少无关，这损害了胎儿生长。
