Faculty Veterinary Medicine, Department of Farm Animal Health, Utrecht University, 3584 CL the Netherlands.
J Dairy Sci. 2010 Dec;93(12):5696-706. doi: 10.3168/jds.2010-3161.
The aim of this study was to evaluate, retrospectively, which physiological states influenced the effect of vitamin E supplements during the dry period on the level of oxidative stress at 2 wk antepartum. Furthermore the effect of oxidative stress at 2 wk antepartum on the risk of clinical mastitis in early lactation was investigated. Cows experience oxidative stress around calving. Vitamin E is able to decrease oxidative stress by scavenging free radicals. Normally, vitamin E radicals formed when vitamin E reacts with free radicals are regenerated by a network of other antioxidants, termed the "vitamin E regeneration system" (VERS). In case of vitamin E supplementation, VERS should be sufficient to regenerate formed vitamin E radicals; if not, oxidative stress might increase instead of decrease. Additionally, the level of oxidative stress and vitamin E might be important physiological states to evaluate before supplementation. In a clinical trial, 296 cows on 5 farms were randomly divided into 2 groups, supplemented with a mineral mix between dry off and calving that supplied 3,000 or 135 IU/d, respectively. Blood samples collected at dry off and 2 wk antepartum were analyzed for vitamin E, reactive oxygen metabolites, ferric-reducing ability of plasma, glutathione peroxidase, and malondialdehyde. Cows were allocated retrospectively into 8 subgroups based on the level of oxidative stress, vitamin E, and VERS status at dry off. To evaluate whether differences in physiological states at dry off influenced the effect of vitamin E supplementation on the level of oxidative stress, group effects (supplemented vs. control) were studied with Student's t-test for all 8 subgroup at 2 wk antepartum. Differences in physiological states at dry off influenced the effect of vitamin E supplements. In 2 insufficient VERS subgroups, the supplemented group had higher levels of free radicals at 2 wk antepartum compared with the control group. Relative risk calculation was used to study the effect of oxidative stress at 2 wk antepartum on the incidence of mastitis in the first 100 d of lactation. Higher levels of oxidative stress at 2 wk antepartum were related to higher risk of clinical mastitis. In conclusion, not every dry cow responded well to high vitamin E supplementation. This subgroup analysis provides a possible explanation for the unexpected adverse effects observed in the clinical trial.
本研究旨在回顾性评估在干奶期补充维生素 E 对产前 2 周氧化应激水平的影响，以及产前 2 周的氧化应激水平对泌乳早期临床乳腺炎发病风险的影响。奶牛在分娩前后会经历氧化应激。维生素 E 通过清除自由基来降低氧化应激。通常，当维生素 E 与自由基反应时，维生素 E 自由基会被称为“维生素 E 再生系统”（VERS）的其他抗氧化剂网络再生。如果进行维生素 E 补充，则 VERS 应该足以再生形成的维生素 E 自由基；如果不是，则氧化应激可能会增加而不是减少。此外，在补充之前，氧化应激水平和维生素 E 可能是需要评估的重要生理状态。在一项临床试验中，将 5 个牧场的 296 头奶牛随机分为 2 组，分别在干奶至分娩期间补充含有 3000 或 135IU/d 的矿物质混合物。在干奶和产前 2 周采集血样，分析维生素 E、活性氧代谢物、血浆还原能力、谷胱甘肽过氧化物酶和丙二醛。根据干奶时的氧化应激、维生素 E 和 VERS 状态，将奶牛回顾性地分配到 8 个亚组中。为了评估干奶时生理状态的差异是否影响维生素 E 补充对氧化应激水平的影响，对产前 2 周的所有 8 个亚组，用学生 t 检验研究组间效应（补充组与对照组）。干奶时生理状态的差异影响维生素 E 补充的效果。在 2 个 VERS 不足的亚组中，与对照组相比，补充组在产前 2 周的自由基水平更高。相对风险计算用于研究产前 2 周的氧化应激水平对泌乳早期前 100 天乳腺炎发病率的影响。产前 2 周氧化应激水平较高与临床乳腺炎的高发病风险相关。总之，并非每头干奶牛对高维生素 E 补充都有良好的反应。本亚组分析为临床试验中观察到的意外不良反应提供了可能的解释。
