Department of Ruminant Science, Institute of Animal Sciences, Volcani Center, PO Box 6, Bet-Dagan 50250, Israel.
J Anim Sci. 2012 Jan;90(1):318-24. doi: 10.2527/jas.2011-3905. Epub 2011 Aug 26.
Ewes bearing more than 1 fetus are more susceptible to pregnancy toxemia than those with a single fetus. Crossbreeding programs in Israel increased the occurrences of ewes bearing more than 2 fetuses; therefore, the aim was to assess the exacerbation in the metabolic status of ewes pregnant with several fetuses. Fifty ewes, genetically developed to achieve multiple-fetus pregnancies, were monitored, on average, from d 115 of pregnancy until lambing for plasma concentrations of several key metabolites and insulin. The numbers of fetuses were examined by ultrasonography at 35 d of pregnancy. Blood samples were collected weekly, and concentrations of glucose, β-hydroxybutyrate (BHBA), NEFA, triglycerides, cholesterol, total calcium, and insulin were determined. The average litter size was 2.75 (±1.1), and 1 (1F), 2 (2F), 3 (3F), and 4 or more (4F) fetuses were conceived, respectively, by 6 (12%), 17 (34%), 14 (28%), and 13 (26%) ewes. Total birth weights of lambs were 6.1, 9.5, 12.7, and 15.0 kg for 1F, 2F, 3F, and 4F, respectively (P < 0.001). Plasma glucose concentrations in 1F were greater than those in 3F and 4F (P < 0.05) and were similar among 2F, 3F, and 4F. Trends toward increasing plasma concentrations of BHBA and NEFA were observed as the number of fetuses increased and also as lambing approached. Plasma concentrations of BHBA and NEFA were, respectively, 3.7 (P < 0.002) and 2.1 (P < 0.001) times as great in 4F ewes as in 1F ewes. Trends toward decreased concentrations of triglycerides and cholesterol were observed as litter size increased. Insulin concentrations in blood decreased considerably as the numbers of fetuses increased and, on average, they were less by a factor of 5 in the 4F ewes than in the 1F ewes (P < 0.001). Moreover, insulin concentrations during the week before lambing were extremely low (e.g., 0.54 µIU/mL in the 4F ewes). Insulin concentrations were reduced in ewes bearing >3 fetuses, even 5 wk before lambing; this decline apparently began earlier than the last month of gestation. Therefore, it seems that insulin has a pivotal role in the etiology of pregnancy ketonemia in ewes carrying multiple fetuses. The present findings may suggest that the decline in insulin concentrations that apparently occurs in the earlier stages of pregnancy represents a homeorhetic control to spare glucose for the brains and fetoplacental units of the dams. The results clearly demonstrate the increased susceptibility to pregnancy toxemia of ewes carrying multiple fetuses. Appropriate nutritional strategies should be developed for ewes that conceive >3 fetuses, to meet the increased nutritional requirements of the fetoplacental unit.
多胎妊娠的母羊比单胎妊娠的母羊更容易患妊娠毒血症。以色列的杂交计划增加了多胎妊娠母羊的数量；因此，目的是评估多胎妊娠母羊代谢状况的恶化。
监测了 50 只经基因改良以实现多胎妊娠的母羊，从妊娠第 115 天到分娩，平均每周监测一次血浆中几种关键代谢物和胰岛素的浓度。在妊娠 35 天时通过超声检查检查胎儿数量。每周采集血样，测定葡萄糖、β-羟丁酸（BHBA）、非酯化脂肪酸（NEFA）、甘油三酯、胆固醇、总钙和胰岛素的浓度。平均产羔数为 2.75（±1.1）只，分别有 1 只（1F）、2 只（2F）、3 只（3F）和 4 只或更多（4F）胎儿受孕，分别有 6 只（12%）、17 只（34%）、14 只（28%）和 13 只（26%）母羊受孕。1F、2F、3F 和 4F 羔羊的总出生体重分别为 6.1、9.5、12.7 和 15.0 公斤（P<0.001）。1F 母羊的血浆葡萄糖浓度高于 3F 和 4F（P<0.05），2F、3F 和 4F 之间的血浆葡萄糖浓度相似。随着胎儿数量的增加和接近分娩，血浆 BHBA 和 NEFA 浓度呈上升趋势。BHBA 和 NEFA 浓度分别在 4F 母羊中是 1F 母羊的 3.7 倍（P<0.002）和 2.1 倍（P<0.001）。随着产羔数的增加，甘油三酯和胆固醇的浓度呈下降趋势。随着胎儿数量的增加，血液中的胰岛素浓度显著降低，平均而言，4F 母羊的胰岛素浓度比 1F 母羊低 5 倍（P<0.001）。此外，在产羔前一周，胰岛素浓度极低（例如，4F 母羊的胰岛素浓度为 0.54 µIU/mL）。在产羔前 5 周，携带>3 只胎儿的母羊的胰岛素浓度降低；这种下降似乎比妊娠最后一个月更早开始。因此，胰岛素似乎在多胎妊娠母羊酮血症的发病机制中起着关键作用。本研究结果可能表明，在妊娠早期明显发生的胰岛素浓度下降代表了一种同型平衡控制，以节省葡萄糖供母体的大脑和胎胎盘单位使用。研究结果清楚地表明，多胎妊娠的母羊更容易患妊娠毒血症。应该为多胎妊娠的母羊制定适当的营养策略，以满足胎胎盘单位对营养的增加需求。
