Ruminant and Swine Clinic, Free University of Berlin, 14163 Berlin, Germany; Technologie und Produktentwicklung Dr. Pieper GmbH, 16818 Wuthenow, Germany.
Ruminant and Swine Clinic, Free University of Berlin, 14163 Berlin, Germany; Institute for Veterinary Epidemiology and Biostatistics, Free University of Berlin, 14163 Berlin, Germany.
J Dairy Sci. 2017 Sep;100(9):7710-7719. doi: 10.3168/jds.2016-12133. Epub 2017 Jul 6.
Glucose is essential for numerous cellular functions due to its involvement in energy supply from early development to adulthood. In the lactating cow, glucose demands by the mammary gland significantly increase to support milk production when compared with other tissues. Thus, insufficient blood glucose levels might predispose dairy cows to metabolic disturbances. The intravenous glucose tolerance test (ivGTT) is a suitable tool to characterize glucose metabolism and insulin responses, but results must be reliable and repeatable. One factor influencing ivGTT is food deprivation period, which has been considered as an obligatory requirement before conduction of glucose tolerance studies in monogastric species, whereas it has been permissive in ruminants. The objective of this study was to determine the influence of 5 fasting periods (0, 12, 24, 36, and 48 h) on ivGTT traits and insulin responses in German Holstein heifers. A total of 140 tests were conducted in 28 females aged 12 to 19 mo. Blood samples were collected every 7 min within 1 h. Assessed glucose and insulin parameters included basal serum glucose and insulin concentration, maximum glucose and insulin concentration obtained between min 7 to 21, and concentrations at min 63 (last sampling) relative to glucose administration, glucose area equivalent (GA), glucose area under the curve (GAUC), insulin area equivalent (InsA), insulin area under the curve (InsAUC), and blood glucose half-life time (GHLT). Serum glucose and insulin concentration were measured according to the hexokinase colorimetric method and solid phase radio immunoassay, respectively. The generalized linear mixed model was used to test for significant differences in all glucose traits and insulin responses at different fasting periods. The model used season and weight as confounding variables. Glucose and insulin concentrations at 0, 7 to 21 (maximum concentration), and 63 min were affected by the duration of food deprivation. The GA, InsA, GAUC, InsAUC, and especially GHLT were also affected by fasting period. A positive linear relationship between GHLT and length of food deprivation was found. Significantly higher GA, GAUC, GHLT values, and glucose and insulin concentration at min 63 were obtained at increasing fasting periods. High intraclass correlation coefficient (0.48) was found for GHLT. The results demonstrate that GHLT might be used to reliably characterize an individual's glucose metabolism and the importance of standardizing food deprivation schedules when performing an ivGTT in nongestating Holstein heifers.
葡萄糖对于从早期发育到成年的许多细胞功能都是必不可少的，因为它参与了能量供应。在泌乳奶牛中，与其他组织相比，乳腺对葡萄糖的需求显著增加，以支持产奶。因此，血糖水平不足可能使奶牛容易发生代谢紊乱。静脉葡萄糖耐量试验（ivGTT）是一种用于描述葡萄糖代谢和胰岛素反应的合适工具，但结果必须可靠且可重复。影响 ivGTT 的一个因素是禁食期，在单胃动物的葡萄糖耐量研究中，这被认为是必需的要求，而在反刍动物中则是允许的。本研究的目的是确定在德国荷斯坦奶牛中，5 个禁食期（0、12、24、36 和 48 小时）对 ivGTT 特征和胰岛素反应的影响。在 28 头 12 至 19 月龄的雌性中进行了总共 140 次测试。在 1 小时内每隔 7 分钟采集一次血样。评估的葡萄糖和胰岛素参数包括基础血清葡萄糖和胰岛素浓度、在第 7 至 21 分钟之间获得的最大葡萄糖和胰岛素浓度以及在第 63 分钟（最后一次采样）相对于葡萄糖给药的浓度、葡萄糖等效面积（GA）、葡萄糖曲线下面积（GAUC）、胰岛素等效面积（InsA）、胰岛素曲线下面积（InsAUC）和血糖半衰期（GHLT）。根据己糖激酶比色法和固相放射免疫分析法分别测量血清葡萄糖和胰岛素浓度。使用广义线性混合模型测试不同禁食期所有葡萄糖特征和胰岛素反应的显著差异。该模型使用季节和体重作为混杂变量。禁食 0、7 至 21 分钟（最大浓度）和 63 分钟时的葡萄糖和胰岛素浓度受禁食时间的影响。GA、InsA、GAUC、InsAUC 尤其是 GHLT 也受到禁食期的影响。发现 GHLT 与禁食时间呈正线性关系。随着禁食期的延长，GA、GAUC、GHLT 值以及第 63 分钟时的葡萄糖和胰岛素浓度显著升高。GHLT 的组内相关系数（0.48）较高。结果表明，GHLT 可用于可靠地描述个体的葡萄糖代谢，并在非妊娠荷斯坦奶牛中进行 ivGTT 时，标准化禁食时间表的重要性。
