Abstract Our study investigates metabolic changes occurring at dry-off and the contribution of milk yield (MY) in such alterations. Thirteen Holsteins were dried off at 55 days from expected calving day (assumed as 0 days from dry-off, DFD) and divided in two groups according to their average daily MY in the last week of lactation, assuming a cut-off of 15 kg·d−1: low MY (7 cows) and high MY (6 cows). From −7 to 34 DFD dry matter intake (DMI) and rumination time were measured. Blood samples were collected at −7, 2, 7, 27 and 34 DFD to assess an haematological and metabolic profile and at −7, 7 and 34 DFD to test functions of circulating white blood cell (WBC) through ex vivo challenges. Data were included in a mixed model for repeated measures assuming MY at dry-off, time and their interaction as fixed effects. After dry-off, DMI was reduced and rumination time was increased in all the animals. High MY cows had greater DMI and rumination time than low MY cows. In blood, WBC counts decreased at 7 DFD and increased the production of pro-inflammatory cytokines at 7 and 34 DFD. Plasmatic concentrations of liver enzymes indicators, positive acute phase proteins (APPs); and nitrogen species increased after dry-off. Conversely, negative APPs and antioxidant species decreased. Those alterations were more marked in high MY animals. This study suggests that dry-off decreased liver function, triggered a systemic inflammation and depleted antioxidant systems, especially in the group of cows with high MY at dry-off. Highlights Inflammation, liver dysfunctions and altered redox balance has been detected after dry-off in all the animals. Cows with highest milk yield before halting of milk removal faced the most severe metabolic challenges. Such founding indicates the management of dry-off as a key point for dairy cows health.

中文翻译：

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高产奶牛断奶时的炎症状态和代谢变化

摘要 我们的研究调查了干奶时发生的代谢变化以及产奶量 (MY) 在此类变化中的贡献。13 只荷斯坦奶牛在预计产犊日后 55 天（假设为 0 天，DFD）被晒干，并根据它们在泌乳最后一周的平均每日 MY 分成两组，假设截止日期为 15 公斤·d−1：低MY（7头奶牛）和高MY（6头奶牛）。测量了 -7 至 34 DFD 的干物质摄入量 (DMI) 和反刍时间。在 -7、2、7、27 和 34 DFD 收集血液样本以评估血液学和代谢特征，并在 -7、7 和 34 DFD 收集血液样本以通过体外挑战测试循环白细胞 (WBC) 的功能。数据包含在一个混合模型中，用于重复测量，假设 MY 在干燥、时间和它们的相互作用作为固定效应。晾干后，所有动物的 DMI 减少，反刍时间增加。高 MY 奶牛比低 MY 奶牛具有更大的 DMI 和反刍时间。在血液中，白细胞计数在 7 DFD 时减少，并在 7 和 34 DFD 时增加促炎细胞因子的产生。肝酶指标、阳性急性期蛋白 (APP) 的血浆浓度；干燥后氮种类增加。相反，负 APP 和抗氧化剂种类减少。这些改变在高 MY 动物中更为显着。这项研究表明，干奶会降低肝功能，引发全身炎症并耗尽抗氧化系统，特别是在干奶时 MY 高的奶牛组中。亮点 在所有动物干燥后都检测到炎症、肝功能障碍和氧化还原平衡改变。停奶前产奶量最高的奶牛面临着最严重的代谢挑战。这表明干奶管理是奶牛健康的关键。