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. 2018 Jan;101(1):774-782. doi: 10.3168/jds.2017-13215. Epub 2017 Nov 6.
Glucose metabolism in dairy and beef cattle has received considerable attention because balanced blood glucose is essential for numerous processes, such as milk production and general health. The glucose tolerance test measures the ability of an organism to regulate blood glucose levels. Glucose half-life time (GHLT) has high heritability and could serve as a potential parameter to breed for metabolic resistance. However, studies focusing on identification of an adequate glucose dose have not yet been conducted in cattle. The objective of this study was to analyze the effect of 5 different glucose doses (0.5, 1, 1.5, 2, and 3 g/kg of body weight) on intravenous glucose tolerance test (ivGTT) traits and insulin responses in nongestating heifers. A total of 150 tests were performed in 30 Holstein-Friesian heifers aged 13 to 15 mo. Blood samples were obtained every 7 min after glucose injection until min 63. Glucose traits and insulin parameters included blood serum glucose and insulin concentration at min 0 (basal concentration), min 7 to 21 (peak glucose and insulin concentration), and min 63 (last sampling) relative to glucose administration, glucose and insulin area under the curve (GAUC and IAUC), and GHLT estimated between min 14 and 42. Serum glucose and insulin concentrations were measured according to the hexokinase colorimetric method and radioimmunoassay, respectively. Generalized linear mixed model was used to test for significant differences in ivGTT traits, insulin responses, and glucose elimination rates (k) over time at different glucose doses. Maximum glucose and insulin concentrations at min 63 increased with higher glucose doses. Significantly lower GHLT were obtained at increasing glucose doses, whereas GAUC and IAUC were significantly higher at increasing doses. The k values were affected by glucose dose and by time interval. Glucose dose greatly affected most ivGTT traits, insulin responses, and glucose elimination rates. Therefore, researchers should standardize their methods to achieve repeatable results and use the same time points for GHLT calculation. Higher glucose doses (≥1.5 g/kg of body weight) triggered glucose concentrations above the glucose renal threshold during the initial 42 min, whereas the lowest glucose concentration failed to induce a maximum insulin response. Further research is necessary to determine an adequate dose inducing maximum insulin responses with minimum renal glucose losses.
奶牛的葡萄糖代谢一直受到广泛关注，因为平衡的血糖水平对于许多过程至关重要，如产奶和整体健康。葡萄糖耐量试验（GTT）用于测量机体调节血糖水平的能力。葡萄糖半衰期（GHLT）具有较高的遗传力，可作为代谢抗性选育的潜在参数。然而，目前尚未在牛中进行确定合适葡萄糖剂量的研究。本研究旨在分析 5 种不同葡萄糖剂量（0.5、1、1.5、2 和 3 g/kg 体重）对非妊娠小母牛静脉葡萄糖耐量试验（ivGTT）特征和胰岛素反应的影响。对 30 头年龄为 13 至 15 月龄的荷斯坦弗里森小母牛进行了 150 次试验。在葡萄糖注射后每 7 分钟采集一次血样，直到第 63 分钟。葡萄糖特征和胰岛素参数包括血清葡萄糖和胰岛素浓度在葡萄糖给药后的第 0 分钟（基础浓度）、第 7 至 21 分钟（葡萄糖和胰岛素浓度峰值）和第 63 分钟（最后一次采样），以及葡萄糖和胰岛素曲线下面积（GAUC 和 IAUC），和第 14 至 42 分钟之间估计的 GHLT。血清葡萄糖和胰岛素浓度分别采用己糖激酶比色法和放射免疫法测定。使用广义线性混合模型检测不同葡萄糖剂量下 ivGTT 特征、胰岛素反应和葡萄糖消除率（k）随时间的显著差异。在第 63 分钟时，最大葡萄糖和胰岛素浓度随葡萄糖剂量的增加而增加。随着葡萄糖剂量的增加，GHLT 显著降低，而 GAUC 和 IAUC 随着剂量的增加而显著增加。k 值受葡萄糖剂量和时间间隔的影响。葡萄糖剂量极大地影响了大多数 ivGTT 特征、胰岛素反应和葡萄糖消除率。因此，研究人员应标准化他们的方法以获得可重复的结果，并使用相同的时间点来计算 GHLT。较高的葡萄糖剂量（≥1.5 g/kg 体重）在最初的 42 分钟内引起了血糖浓度超过肾脏葡萄糖阈值，而最低的葡萄糖浓度未能引起最大的胰岛素反应。需要进一步研究以确定合适的剂量，在最小的肾葡萄糖损失下诱导最大的胰岛素反应。
