Previous work led to the proposal that the precision feeding of a high-concentrate diet may represent a potential method with which to enhance feed efficiency (FE) when rearing dairy heifers. However, the physiological and metabolic mechanisms underlying this approach remain unclear. This study used metabolomics analysis to investigate the changes in plasma metabolites of heifers precision-fed diets containing a wide range of forage to concentrate ratios. Twenty-four half-sib Holstein heifers, with a similar body condition, were randomly assigned into four groups and precision fed with diets containing different proportions of concentrate (20%, 40%, 60% and 80% based on DM). After 28 days of feeding, blood samples were collected 6 h after morning feeding and gas chromatography time-of-flight/MS was used to analyze the plasma samples. Parameters of oxidative status were also determined in the plasma. The FE (after being corrected for gut fill) increased linearly (P < 0.01) with increasing level of dietary concentrate. Significant changes were identified for 38 different metabolites in the plasma of heifers fed different dietary forage to concentrate ratios. The main pathways showing alterations were clustered into those relating to carbohydrate and amino acid metabolism; all of which have been previously associated with FE changes in ruminants. Heifers fed with a high-concentrate diet had higher (P < 0.01) plasma total antioxidant capacity and superoxide dismutase but lower (P ≤ 0.02) hydroxyl radical and hydrogen peroxide than heifers fed with a low-concentrate diet, which might indicate a lower plasma oxidative status in the heifers fed a high-concentrate diet. Thus, heifers fed with a high-concentrate diet had higher FE and antioxidant capacity but a lower plasma oxidative status as well as changed carbohydrate and amino acid metabolism. Our findings provide a better understanding of how forage to concentrate ratios affect FE and metabolism in the precision-fed growing heifers.

先前的工作提出了高精饲料的精确饲喂可能代表一种提高饲料效率的潜在方法（FE) 饲养奶牛时。然而，这种方法背后的生理和代谢机制仍不清楚。本研究使用代谢组学分析来研究含有广泛粗料与精料比例的小母牛精确饲喂日粮血浆代谢物的变化。将 24 头身体状况相似的半同胞荷斯坦小母牛随机分为四组，并精确饲喂含有不同比例精料（基于 DM 为 20%、40%、60% 和 80%）的日粮。喂食 28 天后，早上喂食 6 小时后采集血样，并使用气相色谱飞行时间/MS 分析血浆样品。还测定了血浆中的氧化状态参数。FE（经过肠道填充校正后）线性增加（P< 0.01) 随着膳食浓缩物水平的增加。在饲喂不同日粮草料与精料比例的小母牛血浆中，38 种不同代谢物发生了显着变化。显示改变的主要途径集中在与碳水化合物和氨基酸代谢有关的途径中；所有这些以前都与反刍动物的 FE 变化有关。饲喂高浓度日粮的小母牛血浆总抗氧化能力和超氧化物歧化酶较高（ P < 0.01），但较低（ P≤ 0.02) 羟基自由基和过氧化氢比饲喂低浓度日粮的小母牛，这可能表明饲喂高浓度日粮的小母牛血浆氧化状态较低。因此，饲喂高浓度日粮的小母牛具有较高的 FE 和抗氧化能力，但血浆氧化状态较低，并且碳水化合物和氨基酸代谢发生变化。我们的研究结果更好地理解了粗饲料与精饲料的比例如何影响精确饲喂成长中的小母牛的 FE 和新陈代谢。