BACKGROUND Overgrazing is a primary contributor to severe reduction in forage quality and production in Inner Mongolia, leading to extensive ecosystem degradation, sheep health impairment and growth performance reduction. Further studies to identify serum biomarkers that reflect changes in sheep health and nutritional status following overgrazing would be beneficial. We hereby hypothesize that reduced sheep growth performance under overgrazing conditions would be associated with metabolic and immune response alterations. This study used an untargeted metabolomics analysis by conducting ultra-high-performance liquid chromatography combined with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) of sheep serum under overgrazing and light grazing conditions to identify metabolic disruptions in response to overgrazing. RESULTS The sheep body weight gains as well as serum biochemical variables associated with immune responses and nutritional metabolism (immunoglobulin G, albumin, glucose, and nonesterified fatty acids) were significantly decreased with overgrazing compared with light grazing condition. In contrast, other serum parameters such as alanine and aspartate aminotransferase, alkaline phosphatase, total bilirubin, blood urea nitrogen, and interleukin-8 were markedly higher in the overgrazing group. Principal component analysis discriminated the metabolomes of the light grazing from the overgrazing group. Multivariate and univariate analyses revealed changes in the serum concentrations of 15 metabolites (9 metabolites exhibited a marked increase, whereas 6 metabolites showed a significant decrease) in the overgrazing group. Major changes of fatty acid oxidation, bile acid biosynthesis, and purine and protein metabolism were observed. CONCLUSIONS These findings offer metabolic evidence for putative biomarkers for overgrazing-induced changes in serum metabolism. Target-identification of these particular metabolites may potentially increase our knowledge of the molecular mechanisms of altered immune responses, nutritional metabolism, and reduced sheep growth performance under overgrazing conditions.

中文翻译：

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过度放牧或轻度放牧条件下绵羊血清变化的比较代谢组学分析。

背景技术过度放牧是内蒙古牧草质量和产量严重下降的主要原因，导致广泛的生态系统退化，绵羊健康受损和生长性能下降。进一步研究以鉴定反映过度放牧后绵羊健康和营养状况变化的血清生物标志物将是有益的。我们据此假设，过度放牧条件下绵羊生长性能的下降将与代谢和免疫反应的改变有关。这项研究采用超目标液相色谱结合超高放牧和光放牧条件下绵羊血清的四极杆飞行时间质谱（UHPLC-Q-TOF / MS）进行了非目标代谢组学分析，以识别代谢破坏过度放牧 结果与轻度放牧相比，过度放牧绵羊的体重增加以及与免疫反应和营养代谢相关的血清生化变量（免疫球蛋白G，白蛋白，葡萄糖和非酯化脂肪酸）显着降低。相反，过度放牧组的其他血清参数，如丙氨酸和天冬氨酸转氨酶，碱性磷酸酶，总胆红素，血尿素氮和白介素8则明显更高。主成分分析区分了过度放牧组中轻度放牧的代谢组。多变量和单变量分析显示，过度放牧组的血清中15种代谢物的浓度发生了变化（9种代谢物表现出明显的增加，而6种代谢物表现出明显的减少）。观察到脂肪酸氧化，胆汁酸生物合成以及嘌呤和蛋白质代谢的主要变化。结论这些发现为过度放牧引起的血清代谢变化的推定生物标志物提供了代谢证据。这些特定代谢物的目标识别可能会增加我们对过度放牧条件下免疫反应改变，营养代谢和绵羊生长性能下降的分子机制的了解。