Abstract
BackgroundOvergrazing 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.ResultsThe 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.ConclusionsThese 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.
Highlights
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
Liquid chromatography/mass spectrometry (LC/MS)-based metabolomics was used to compare the metabolisms of sheep under light grazing (LG) and OG conditions, which will provide a comprehensive overview of the metabolic profile to help understand the molecular mechanisms of reduced animal growth performance in response to OG
We found that several differentially expressed hepatic genes related to the peroxisome proliferator-activated receptor (PPAR) pathway and fatty acid oxidation were significantly upregulated in the OG sheep
Summary
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. We hereby hypothesize that reduced sheep growth performance under overgrazing conditions would be associated with metabolic and immune response alterations. In response to overgrazing induced undernutrition, the long-term response of animal was characterized by nutrients mobilization (energy, protein and so on), which triggered tissue masses decrease, especially fat and muscle tissues. This may be a primary reason for the reduced growth performance observed in overgrazing sheep. A number of metabolites related to sheep immune responses and nutritional metabolism may be altered by overgrazing induced forage degradation and lower animal growth performance. Few quantitative data are available on the metabolic profile alterations of sheep under overgrazing conditions
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