Potential and Limitations of plant polyphenols to reduce methane emissions from ruminants in grassland systems

反刍动物农业的甲烷排放量占欧盟27国温室气体排放量的12-17%。然而，在欧洲，减少这些排放的可能性是有限的，而不会降低动物的生产力。现有的几个可能性之一是饲料植物含有单宁。虽然关于这一主题的研究已经进行了几年，但关于牧草物种减少甲烷排放的潜力的结果差异很大。这阻止了含单宁的饲料植物在农业中的广泛应用，尽管增加草原生物多样性的有益副作用。观察到的抗产甲烷潜力的变化的主要原因之一是，以前的实验通常只定量总酚化合物。这是有问题的，因为它忽略了单宁的结构特征，这已被证明会显著影响生物活性。此外，只分析了极少数物种，而且是在池样品中，而不是在个别植物中，因此忽略了物种内的变异性，使以前的结果更难以解释。然而，最近的进展，在分析单宁允许更快，更好的分析单宁浓度和它们的结构特征。此外，这些新的方法允许同时定量黄酮类化合物或其他多酚类化合物，这些多酚类化合物具有潜在的生物活性，可能也存在于饲料物种中。i）单宁的准确和改进的表征将允许改进对它们的抗产甲烷潜力的评估，ii）这些单宁的作用可以减少或增加，依赖于额外的多酚的共存，和iii）生长条件的差异影响了先前研究中的单宁含量，因此难以在这些研究之间进行比较。为了解决这些问题，我们将在相同的环境条件下培养8种含单宁牧草品种的不同个体，然后用最现代化的设备分析其生物活性化合物。此外，将使用Hohenheim气体测试对其甲烷还原潜力进行量化。对本实验的实验设计进行了优化，用于化学表征与观察到的生物活性之间联系的统计分析，并允许将结果外推至其他物质。最后，在本实验中，我们将首次分析蛋白质和纤维结合的单宁，因为它们可能有助于抗甲烷作用。因此，本研究为后续的体内试验提供了良好的基础。本研究项目受益于小组成员在植物化学分析以及牧草生产、草地系统和动物营养方面的经验。

Methane emissions from ruminant agriculture account for 12-17% of all EU-27 GHG emissions. However, possibilities to reduce these emissions are limited in Europe without risking decrements in the animal’s productivity. One of the few existing possibilities is the feeding of forage plants that contain tannins. Although research on this topic has been conducted for several years already, results about the potential of forage species to reduce methane emissions were highly variable. This prevented a widespread application of tannin-containing forage plants in agriculture, despite the beneficial side effect of increasing grassland biodiversity. One of the main reasons for the observed variability in antimethanogenic potential is that previous experiments usually only quantified total phenolic compounds. This is problematic as it ignores the structural characteristics of tannins, which have been proven to affect the bioactivity substantially. Additionally, only very few species were analysed and also in pool samples rather than individual plants, hence ignoring the variability within species and making previous results even more difficult to interpret. Nevertheless, recent advances in the analysis of tannins permitted faster and better analyses of both tannin concentration and their structural characteristics. Additionally, these new methods permit a simultaneous quantification of flavonoids or other polyphenols with potential bioactivity that might be present in the forage species as well.We put forward the following hypotheses: i) an accurate and improved characterisation of tannins will permit an improved assessment of their antimethanogenic potential, ii) the effect of these tannins can be reduced or increased, dependent on the co-presence of additional polyphenols, and iii) differences in growing conditions have affected the tannin content in previous studies, thus making comparisons among these studies difficult. To solve these issues, we will cultivate different individuals of several cultivars from eight tannin containing forage species under identical environmental conditions, and subsequently analyse their bioactive compounds with the most modern equipment available. Furthermore, their methane reducing potential will be quantified using the Hohenheim gas test. The experimental design for this experiment was optimized for the statistical analysis of the link between the chemical characterization and the observed bioactivity, and to permit extrapolation of results to additional species. Finally, in this experiment, we will analyse protein and fibre bound tannins for the first time, as they might contribute to the ant-methanogenic effect. Hence, this study provides an excellent basis for subsequent in vivo trials.This research project benefits from the experience of the group members in phytochemical analyses, as well as regarding forage production, grassland systems and animal nutrition.