In the present study, we tested the hypothesis that overconditioning in dairy cows at the end of the dry period leads to infiltration of fat and alterations of the insulin secretory capacity of the pancreas. Pregnant Holstein Friesian dairy cows were selected based on body condition score (BCS) at the start of the dry period. Body condition score varied between cows to have optimal conditioned (2.5 < BCS ≤3.5, n = 5) and overconditioned (3.5 < BCS ≤5, n = 5) cows. All animals underwent an intravenous glucose tolerance test (IVGTT) at an average of 260 d of gestation to measure the pancreatic insulin secretory capacity and assess peripheral insulin sensitivity regarding glucose metabolism. Eight days after the IVGTT, animals were slaughtered. The pancreas was dissected and weighed and tissue samples were taken for histological analysis. Results revealed that overconditioning in dairy cows led to fat infiltration in the pancreas and an increase in size of pancreatic islets expressed relative to the total area of pancreatic tissue. In addition, results revealed a positive correlation between serum fatty acid concentration and peak insulin concentration and area and number of pancreatic islets expressed relative to the total area of pancreatic tissue. The IVGTT revealed that overconditioned animals have a higher insulin secretory capacity of the pancreas, as demonstrated by higher peak insulin concentration, higher acute insulin response to glucose, and higher area under the curve (AUC) for insulin compared with optimal conditioned cows. A higher AUC for glucose during the first 60 min following administration of the glucose bolus in overconditioned cows indicates an insulin-resistant state regarding glucose metabolism. Our results suggest that the pancreas of overconditioned dairy cows at the end of gestation compensates for the concomitantly elevated level of peripheral insulin resistance by greater secretion of insulin.

在本研究中，我们检验了以下假设，即奶牛在干燥期结束时过度调理会导致脂肪渗透和胰腺胰岛素分泌能力的改变。在干燥期开始时，根据身体状况评分（BCS）选择怀孕的荷斯坦黑白花奶牛。母牛的身体状况得分各不相同，其中条件最佳的母牛（2.5 <BCS≤3.5，n = 5）和条件过度的母牛（3.5 <BCS≤5，n = 5）。所有动物均接受静脉内葡萄糖治疗在平均妊娠260 d时进行耐受性试验（IVGTT），以测量胰腺胰岛素分泌能力并评估有关葡萄糖代谢的外周胰岛素敏感性。IVGTT后八天，将动物宰杀。解剖胰腺并称重，并取组织样品进行组织学分析。结果表明，奶牛过度调理导致胰腺中的脂肪浸润，并且相对于胰腺组织总面积而言，所表达的胰岛的大小增加。另外，结果显示血清脂肪酸浓度和峰值胰岛素浓度之间的正相关性以及所表达的胰岛的面积和数量相对于胰组织的总面积呈正相关。IVGTT显示，过度训练的动物胰腺的胰岛素分泌能力更高，与最佳条件牛相比，胰岛素的峰值胰岛素浓度更高，急性胰岛素对葡萄糖的响应更高，曲线下面积（AUC）更高，证明了这一点。在过度调节的母牛中，在给予葡萄糖推注后的最初60分钟内，较高的葡萄糖AUC表示关于葡萄糖代谢的胰岛素抵抗状态。我们的结果表明，妊娠结束时过度适应的奶牛的胰腺会通过增加胰岛素的分泌来补偿随之而来的外周胰岛素抵抗水平的升高。在过度调节的母牛中，在给予葡萄糖推注后的最初60分钟内，较高的葡萄糖AUC表示关于葡萄糖代谢的胰岛素抵抗状态。我们的结果表明，妊娠结束时过度适应的奶牛的胰腺会通过增加胰岛素的分泌来补偿随之而来的外周胰岛素抵抗水平的升高。在过度调节的母牛中，在给予葡萄糖推注后的最初60分钟内，较高的葡萄糖AUC表示关于葡萄糖代谢的胰岛素抵抗状态。我们的结果表明，妊娠结束时过度适应的奶牛的胰腺会通过增加胰岛素的分泌来补偿随之而来的外周胰岛素抵抗水平的升高。