Department of Animal Science, Faculty of Science and Technology, Aarhus University, Foulum, DK-8830 Tjele, Denmark.
J Dairy Sci. 2011 Aug;94(8):3913-27. doi: 10.3168/jds.2010-3724.
The present study aimed to investigate the effects of 2-hydroxy-4-(methylthio)-butanoic acid isopropyl ester (HMBi) supplementation on splanchnic AA metabolism, essential AA (EAA) mobilization, and plasma AA status in postpartum transition dairy cows. The EAA mobilization was calculated by difference: EAA excretion in milk protein - net portal absorption of EAA or net splanchnic release of EAA. Eight Holstein cows fitted with permanent indwelling catheters in the hepatic portal vein, hepatic vein, mesenteric vein, and an artery in the dry period preceding second parturition were used in the study. Cows were randomly allocated to 1 of 4 treatments in a 2×2 factorial arrangement with factor 1: control (calcium carbonate) versus HMBi [1.5 g of HMBi/kg of dry matter (DM)] and factor 2: high dietary ethanol (19 g/kg of DM) versus high dietary propanol (16 g/kg of DM). Only factor 1 data are presented. Treatments were administered in 4 total mixed rations and initiated on the day of parturition. Cows were sampled 14 d before expected parturition and 4, 15, and 29 d after parturition. Supplementation with HMBi tended to increase milk fat content but not fat yield, tended to impose a slower rate of decrease in milk casein content with increasing days in milk (DIM), prevented the decrease in plasma Met associated with parturition for control, reduced plasma concentration of Ser, tended to reduce plasma concentrations of Gly and His, and tended to increase hepatic uptake of Met postpartum. Cows excreted 248±18 g more EAA in the milk at 4 DIM than was released from splanchnic tissues. The EAA deficiency decreased as lactation progressed and was not affected by HMBi supplementation. It was estimated that 4,700±600 g of EAA from extra-splanchnic tissues were secreted in milk protein during the first 29 DIM. Extra-splanchnic EAA mobilization can be crucial to sustain milk protein yield in the postpartum transition period and HMBi is a fast-working Met source that can improve Met status of postpartum transition cows.
本研究旨在探讨 2-羟基-4-(甲硫基)-丁酸异丙酯（HMBi）补充对围产期奶牛内脏 AA 代谢、必需 AA（EAA）动员和血浆 AA 状态的影响。EAA 动员通过差值计算：乳蛋白中 EAA 的排泄量-门静脉净吸收 EAA 或内脏净释放 EAA。在第二次分娩前的干奶期，对 8 头荷斯坦奶牛进行了肝门静脉、肝静脉、肠系膜静脉和动脉的永久性留置导管插入术。奶牛随机分为 4 种处理的 2×2 因子设计，因子 1：对照组（碳酸钙）与 HMBi[1.5 g HMBi/kg 干物质（DM）]和因子 2：高日粮乙醇（19 g/kg DM）与高日粮丙醇（16 g/kg DM）。仅呈现因子 1 数据。处理在 4 个全混合日粮中进行，并在分娩当天开始。奶牛在预期分娩前 14 天和分娩后 4、15 和 29 天采样。HMBi 补充剂可提高乳脂含量，但不提高乳脂产量，随着泌乳天数（DIM）的增加，可减缓乳清蛋白含量的下降速度，防止与分娩相关的血浆 Met 下降，降低与分娩相关的血浆 Met 下降。与对照组相比，降低了血浆 Ser 浓度，降低了血浆 Gly 和 His 浓度，增加了产后肝摄取 Met。奶牛在 4 DIM 时从乳中排出的 EAA 比内脏组织释放的 EAA 多 248±18 g。随着泌乳的进行，EAA 缺乏症逐渐减轻，HMBi 补充剂没有影响。据估计，在最初的 29 DIM 期间，4700±600 g 的 EAA 从内脏组织外分泌到乳蛋白中。围产期过渡期间，EAA 动员对维持乳蛋白产量至关重要，HMBi 是一种快速作用的 Met 来源，可以改善围产期过渡奶牛的 Met 状态。
