Department of Animal Sciences, Universidade Federal de Minas Gerais, Minas Gerais, 30161-970, Brazil; Department of Animal Sciences, Purdue University, West Lafayette, IN 47906.
Department of Animal Sciences, Purdue University, West Lafayette, IN 47906.
J Dairy Sci. 2020 Aug;103(8):7547-7554. doi: 10.3168/jds.2019-17139. Epub 2020 May 29.
The objective for this study was to determine the effect of glucose dose and days following peak milk yield on plasma glucose, serum insulin, and plasma nonesterified fatty acids (NEFA) kinetics during an intravenous glucose tolerance test (IVGTT) in lactating dairy cattle. Six lactating Holstein dairy cows (3 primiparous and 3 multiparous) were assigned to 2 squares and received 0.092, 0.15, or 0.3 g of glucose/kg of body weight (BW) during an IVGTT at 74 and 221 d in milk (DIM), representing early (post-peak) lactation and mid lactation, respectively. Treatments were applied in a replicated Latin square design using contiguous 7-d periods within each stage of lactation. Milk production and dry matter intake were determined daily during the first 6 d of each period. The IVGTT was performed on d 7. For the IVGTT, cows were prepared with indwelling catheters in each jugular vein, and blood samples were collected at -15, -10, 5, 10, 15, 20, 30, 45, 60, 90, and 120 min relative to the glucose infusion. Samples were analyzed for plasma glucose, serum insulin, and plasma NEFA concentrations. Increasing the glucose dose during the IVGTT increased plasma glucose area under the curve (AUC), decreased glucose half-life, and increased maximal plasma glucose concentrations in plasma during the IVGTT. Greater glucose dose during the IVGTT elevated serum insulin AUC and increased nadir NEFA concentrations. Maximal plasma glucose concentration during the IVGTT was lower, whereas maximum NEFA concentration, NEFA AUC, and NEFA clearance rate were greater at 74 than at 221 DIM. Only glucose half-life was responsive to stage of lactation × glucose dose effects during the IVGTT, and the decrease in glucose half-life with increasing glucose dose was greater at 74 than at 221 DIM. Glucose AUC was greater and NEFA AUC lower for cows at 74 than at 221 DIM. For the doses tested, a glucose dose greater than 0.092 g/kg of BW resulted in peak blood glucose concentration that exceeded the previously reported renal glucose excretion threshold of 8.3 mM. There is a need for accompanying data to determine if this is the case for the glucose doses evaluated in this experiment. Based on maximal peak glucose concentrations and effects on glucose half-life, we identify 0.092 g of glucose/kg of BW (0.46 g/kg of metabolic body weight) as the preferred dose for the IVGTT for cows at 74 and 221 DIM in this study.
本研究旨在确定在静脉葡萄糖耐量试验（IVGTT）期间，葡萄糖剂量和产奶高峰后天数对泌乳奶牛血浆葡萄糖、血清胰岛素和血浆非酯化脂肪酸（NEFA）动力学的影响。6 头泌乳荷斯坦奶牛（3 头初产和 3 头经产）被分配到 2 个方，并在产奶第 74 天和 221 天（DIM）接受 0.092、0.15 或 0.3 g/kg 体重的葡萄糖，分别代表早期（产奶高峰后）和中期泌乳。在泌乳阶段的每个连续 7 天内，采用重复拉丁方设计应用处理。在每个时期的前 6 天内，每天测定产奶量和干物质摄入量。IVGTT 在第 7 天进行。对于 IVGTT，在每个颈静脉中准备了留置导管，并在葡萄糖输注前-15、-10、5、10、15、20、30、45、60、90 和 120 分钟时采集血样。样品用于分析血浆葡萄糖、血清胰岛素和血浆 NEFA 浓度。在 IVGTT 期间增加葡萄糖剂量会增加血浆葡萄糖曲线下面积（AUC）、降低葡萄糖半衰期，并增加 IVGTT 期间的最大血浆葡萄糖浓度。IVGTT 期间的葡萄糖剂量增加会升高血清胰岛素 AUC，并增加最低 NEFA 浓度。IVGTT 期间的最大血浆葡萄糖浓度较低，而 74 天的最大 NEFA 浓度、NEFA AUC 和 NEFA 清除率高于 221 天。只有葡萄糖半衰期对 IVGTT 期间的泌乳阶段×葡萄糖剂量效应有反应，并且随着葡萄糖剂量的增加，葡萄糖半衰期的降低在 74 天比在 221 天更明显。74 天的奶牛葡萄糖 AUC 较大，NEFA AUC 较低。对于所测试的剂量，大于 0.092 g/kg BW 的葡萄糖剂量会导致血糖峰值浓度超过先前报道的 8.3 mM 的肾脏葡萄糖排泄阈值。需要伴随数据来确定在本实验中评估的葡萄糖剂量是否如此。基于最大峰值葡萄糖浓度和对葡萄糖半衰期的影响，我们确定 0.092 g/kg BW 的葡萄糖（0.46 g/kg 代谢体重）为该研究中 74 天和 221 天奶牛 IVGTT 的首选剂量。
