ETH Zürich, Department of Environmental Systems Science, Institute of Agricultural Sciences, 8092 Zürich, Switzerland.
ETH Zürich, Department of Chemistry and Applied Biosciences, Analytical Chemistry, 8093 Zürich, Switzerland.
J Dairy Sci. 2023 Oct;106(10):6849-6859. doi: 10.3168/jds.2023-23301. Epub 2023 May 18.
To date, the commonly used methods to assess rumen fermentation are invasive. Exhaled breath contains hundreds of volatile organic compounds (VOC) that can reflect animal physiological processes. In the present study, for the first time, we aimed to use a noninvasive metabolomics approach based on high-resolution mass spectrometry to identify rumen fermentation parameters in dairy cows. Enteric methane (CH) production from 7 lactating cows was measured 8 times over 3 consecutive days using the GreenFeed system (C-Lock Technology Inc.). Simultaneously, exhalome samples were collected in Tedlar gas sampling bags and analyzed offline using a secondary electrospray ionization high-resolution mass spectrometry system. In total, 1,298 features were detected, among them targeted exhaled volatile fatty acids (eVFA; i.e., acetate, propionate, butyrate), which were putatively annotated using their exact mass-to-charge ratio. The intensity of eVFA, in particular acetate, increased immediately after feeding and followed a similar pattern to that observed for ruminal CH production. The average total eVFA concentration was 35.5 count per second (CPS), and among the individual eVFA, acetate had the greatest concentration, averaging 21.3 CPS, followed by propionate at 11.5 CPS, and butyrate at 2.67 CPS. Further, exhaled acetate was on average the most abundant of the individual eVFA at around 59.3%, followed by 32.5 and 7.9% of the total eVFA for propionate and butyrate, respectively. This corresponds well with the previously reported proportions of these VFA in the rumen. The diurnal patterns of ruminal CH emission and individual eVFA were characterized using a linear mixed model with cosine function fit. The model characterized similar diurnal patterns for eVFA and ruminal CH and H production. Regarding the diurnal patterns of eVFA, the phase (time of peak) of butyrate occurred first, followed by that of acetate and propionate. Importantly, the phase of total eVFA occurred around 1 h before that of ruminal CH. This corresponds well with existing data on the relationship between rumen VFA production and CH formation. Results from the present study revealed a great potential to assess the rumen fermentation of dairy cows using exhaled metabolites as a noninvasive proxy for rumen VFA. Further validation, with comparisons to rumen fluid, and establishment of the proposed method are required.
迄今为止，常用的评估瘤胃发酵的方法是有创的。呼气中含有数百种挥发性有机化合物（VOC），可以反映动物的生理过程。在本研究中，我们首次旨在使用基于高分辨率质谱的非侵入性代谢组学方法来识别奶牛的瘤胃发酵参数。使用 GreenFeed 系统（C-Lock Technology Inc.）在连续 3 天的 8 次测量了 7 头泌乳奶牛的肠道甲烷（CH）产量。同时，在 Tedlar 气体采样袋中收集呼气样本，并使用二次电喷雾电离高分辨率质谱系统离线分析。共检测到 1298 种特征，其中靶向呼出挥发性脂肪酸（eVFA；即乙酸、丙酸、丁酸），通过其精确的质荷比进行了推测注释。eVFA 的强度，特别是乙酸，在进食后立即增加，并遵循与瘤胃 CH 生产相同的模式。平均总 eVFA 浓度为 35.5 个计数/秒（CPS），在个体 eVFA 中，乙酸的浓度最大，平均为 21.3 CPS，其次是丙酸为 11.5 CPS，丁酸为 2.67 CPS。此外，呼出的乙酸平均是个体 eVFA 中最丰富的，约为 59.3%，其次是丙酸和丁酸分别占总 eVFA 的 32.5%和 7.9%。这与以前报道的瘤胃中这些 VFA 的比例非常吻合。使用带有余弦函数拟合的线性混合模型来描述瘤胃 CH 排放和个体 eVFA 的昼夜模式。该模型描述了 eVFA 和瘤胃 CH 和 H 产生的相似昼夜模式。关于 eVFA 的昼夜模式，丁酸的相位（峰值时间）首先出现，其次是乙酸和丙酸。重要的是，总 eVFA 的相位大约比瘤胃 CH 提前 1 小时。这与瘤胃 VFA 产生与 CH 形成之间的关系的现有数据非常吻合。本研究的结果表明，使用呼出代谢物作为瘤胃 VFA 的非侵入性替代物来评估奶牛瘤胃发酵具有很大的潜力。需要进一步验证，与瘤胃液进行比较，并建立所提出的方法。
