Metabolomics of high and low feed efficient dairy cows reveal novel physiological mechanisms

Residual feed intake (RFI) is designed to estimate net efficiency of feed use, so low RFI animals are considered for selection purposes of eating less and efficient production. Metabolomics has been increasingly used to measure dynamic metabolic response, while related reports on different concentrated diet (CD) for RFI of dairy cows were scarce. Therefore, the objective of this study is to generate a better understanding of metabolic mechanisms belonging to Jersey or Holstein of two CDs for two RFIs. Gas chromatography - Mass spectrometry (GC-MS) system was used for the annotation of each metabolite. Two feeding period differences of low/high CDs were compared in two breeds and two RFIs. Repeated measures ANOVA was used to evaluate breed, RFI and CD effects on identified metabolites. Integrative analysis of metabolomics and transcriptomics was performed to explore interactions between functionally related metabolites and genes in the created network. Regarding to the comparison between two RFIs, significant (P < 0.001) differences were observed in the amino acid group of second feeding period of Jersey cows and first feeding period of Holstein cows, and in the fatty acid group of second feeding period of Holstein cows. Pyruvic acid was the most significant metabolite (P < 0.001) and a good division appeared after PCA between two feeding periods. Significant breed effect (P < 0.05) was found in Isoleucine, Leucine, Octadecanoic acid, Ornithine, Pentadecanoic acid and Valine, whereas significant RFI effect (P < 0.05) only exited in Leucine. The integrated gene-metabolite pathway analysis showed pathway impact values were higher than single metabolic pathway analysis, but both analysis revealed three important pathways with powerful testing values (Aminoacyl-tRNA biosynthesis, Alanine, aspartate and glutamate metabolism and TCA cycle). Finally, we found four networks that were ELOVL6, LYZ, CTH and HACL1 associated with seven metabolites (α-ketoglutarate, Alanine, Aspartic acid, Methionine, Palmitoleic acid, Pyruvic acid and Succinic acid). Our results provide a good understanding in metabolic mechanisms and summary valuable metabolic pathways and networks with gene expressions in Nordic dairy cows, for example, network of overexpressed ELOVL6 consistent with up-regulated Palmitoleic acid could be applied in further selection programs.