Identification of effects of different forage source on metabolism and function of liver from dairy cows using systematic approaches

Abstract Text:

Liver occupies a unique role in nutritional physiology of lactating dairy cows, but the effects of forage source on its metabolism and function have not been well examined. This study was conducted to investigate the effects of different forage source on liver metabolites and key gene functions in dairy cows using gas chromatography–time of flight/mass spectrometry (GC-TOF/MS) based metabolomics and RNA-seq analysis. A total of 12 multiparous Holstein dairy cows were fed 2 diets with different forage source: Alfalfa hay (AH, n=6) and corn stover (CS, n=6). The multivariate statistical analysis (PCA, PLS-DA, and OPLS-DA) showed a clear separation of metabolomics profiles between AH and CS groups. A total of 270 metabolites were identified in the liver with 28 of them significantly different between the 2 diets (VIP>1&P<0.05). In AH, 71 up-regulated metabolites (log₂(z-score) > 1 & P< 0.05) were associated with gluconeogenesis, vitamin and mineral metabolism, amino acid metabolism, propanoate metabolism, cell death and survival, carbohydrate metabolism, and energy production. In CS, 64 up-regulated metabolites were involved in cellular growth and proliferation, organismal development, cell-to-cell signaling and interaction, molecular transport and lipid metabolism. Three metabolites, leucine, cystine, and hippuric acid were further identified as biomarkers based on the analysis (AUC value, predicted class probabilities, and predicted accuracy) of different combinations of significantly different metabolites. In addition, expression of 11,781 genes was detected (more than 50% of samples with CPM>1) in the liver. One gene module containing 122 genes had a significantly strong positive correlation (R=0.82, P=0.001) with cystine abundance by weighted gene co-expression network analysis (WGCNA). The main functions represented by these genes were gluconeogenesis, pyruvate metabolic process, monosaccharide biosynthetic process, carbohydrate homeostasis, glucose homeostasis, hexose biosynthetic process, chemical homeostasis, and vitamin-related metabolic process which were all up-regulated in the AH group. Our results suggest that various metabolites, pathways, and gene functions were significant changed in response to forage source. These can be used for further characterization of the regulatory mechanisms of forage-related milk performance in dairy cows.

Keywords: dairy cow, gene function, liver metabolomics