Department of Animal Science, Cornell University, Ithaca, NY 14853, USA.
J Dairy Sci. 2012 Feb;95(2):670-82. doi: 10.3168/jds.2011-4529.
Nonlactating Holstein cows (n=12) in late pregnancy were used to determine effects of plane of nutrition followed by feed deprivation on metabolic responses to insulin. Beginning 48 d before expected parturition, cows were fed to either a high plane (HP) or a low plane (LP) of nutrition (162 and 90% of calculated energy requirements, respectively). Cows were subjected to an intravenous glucose tolerance test [GTT; 0.25 g of dextrose/kg of body weight (BW)] on d 14 of treatment and a hyperinsulinemic-euglycemic clamp (HEC; 1 μg/kg of BW/h) on d 15. Following 24 h of feed removal, cows were subjected to a second GTT on d 17 and a second HEC on d 18 after 48 h of feed removal. During the feeding period, plasma nonesterified fatty acid (NEFA) concentrations were higher for cows fed the LP diet compared with those fed the HP diet (163.6 vs. 73.1 μEq/L), whereas plasma insulin was higher for cows fed the HP diet during the feeding period (11.1 vs. 5.2 μIU/mL). Glucose areas under the curve during both GTT were higher for cows fed the LP diet than for those fed the HP diet (4,213 vs. 3,750 mg/dL × 60 min) and was higher during the GTT in the feed-deprived state (4,878 vs. 3,085 mg/dL × 60 min) than in the GTT during the fed state, suggesting slower clearance of glucose during negative energy balance either pre-or post-feed deprivation. This corresponded with a higher dextrose infusion rate during the fed-state HEC than during the feed-deprived-state HEC (203.3 vs. 90.1 mL/h). Plasma NEFA decreased at a faster rate following GTT during feed deprivation compared with that during the fed state (8.7 vs. 2.9%/min). Suppression of NEFA was highest for cows fed the HP diet during the GTT conducted during feed deprivation, and lowest for cows fed the HP diet during the fed-state GTT (68.6 vs. 50.3% decrease from basal). Plasma insulin responses to GTT were affected by feed deprivation such that cows had a much lower insulin response to GTT by 24 h after feed removal (995 vs. 3,957 μIU/mL × 60 min). During the fed-state HEC, circulating concentrations of NEFA were 21% below basal for cows fed the HP diet and 62% below basal for cows fed the LP diet; during feed deprivation, NEFA were 79 and 59% below basal for the HP and LP diets, respectively (diet × HEC). Cows that are fed below energy requirements or are feed deprived have slower clearance of glucose and greater NEFA responses to glucose challenge. Additionally, feed deprivation had a large effect on insulin secretion. Overall, effects of feed deprivation were larger than effects of plane of nutrition.
处于妊娠后期的非泌乳荷斯坦奶牛（n=12）用于确定营养水平和随后的禁食对胰岛素代谢反应的影响。从预计分娩前 48 天开始，奶牛分别以高营养水平（HP）或低营养水平（LP）（分别为计算能量需求的 162%和 90%）进行饲养。在处理的第 14 天，奶牛接受静脉葡萄糖耐量试验[GTT；0.25 克葡萄糖/千克体重（BW）]，第 15 天进行高胰岛素-正常血糖钳夹（HEC；1 μg/kg BW/h）。在禁食 24 小时后，在禁食 48 小时后，奶牛在第 17 天接受第二次 GTT，并在第 18 天接受第二次 HEC。在喂养期间，与饲喂 HP 日粮的奶牛相比，饲喂 LP 日粮的奶牛血浆非酯化脂肪酸（NEFA）浓度更高（163.6 与 73.1 μEq/L），而在喂养期间，饲喂 HP 日粮的奶牛血浆胰岛素水平更高（11.1 与 5.2 μIU/mL）。与饲喂 HP 日粮的奶牛相比，饲喂 LP 日粮的奶牛在两次 GTT 期间的血糖曲线下面积更高（4,213 与 3,750 mg/dL×60 min），在禁食状态下的 GTT 中更高（4,878 与 3,085 mg/dL×60 min），表明在负能平衡状态下，无论是在禁食前还是禁食后，葡萄糖的清除速度都较慢。这与喂养状态下 HEC 时的葡萄糖输注率高于禁食状态下 HEC 时的葡萄糖输注率相对应（203.3 与 90.1 mL/h）。与在喂食状态下相比，在禁食状态下，GTT 后 NEFA 的下降速度更快（8.7%与 2.9%/min）。在禁食状态下进行的 GTT 中，饲喂 HP 日粮的奶牛对 NEFA 的抑制作用最高，而在喂食状态下进行的 GTT 中，饲喂 HP 日粮的奶牛对 NEFA 的抑制作用最低（68.6%与 50.3%的基础值下降）。GTT 对胰岛素的反应受到禁食的影响，以至于在禁食后 24 小时，奶牛对 GTT 的胰岛素反应大大降低（995 与 3,957 μIU/mL×60 min）。在喂养状态下的 HEC 中，饲喂 HP 日粮的奶牛的循环 NEFA 浓度比基础值低 21%，饲喂 LP 日粮的奶牛的循环 NEFA 浓度比基础值低 62%；在禁食期间，HP 和 LP 日粮的 NEFA 分别比基础值低 79%和 59%（日粮×HEC）。饲喂低于能量需求或禁食的奶牛，葡萄糖清除速度较慢，对葡萄糖的 NEFA 反应更大。此外，禁食对胰岛素分泌有很大影响。总体而言，禁食的影响大于营养水平的影响。
