Metabolic mechanism of hepatic steatosis affecting production performance of dairy cows during peak lactation

In order to explore the metabolic mechanism of hepatic steatosis affecting production performance of dairy cows, the physiological and biochemical indexes and transcriptome sequencing results of dairy cows with mild hepatic steatosis were compared and analyzed, with healthy dairy cows used as controls. Histological examination of liver tissue revealed that when steatosis occurred, hematoxylin-eosin stained sections of liver tissue showed nearly round vacuoles of varying sizes. Compared with those of healthy dairy cows, the yields of fat-corrected milk, energy-corrected milk and the milk fat content of dairy cows with mild hepatic steatosis were significantly lower (p＜0.01), and there were no significant differences in plasma biochemical indexes. A total of 241 differentially expressed genes (DEGs) were found in liver by transcriptome sequencing, including 136 down-regulated DEGs and 105 up-regulated DEGs. Gene ontology (GO) functional annotation showed that DEGs were enriched mainly in biological processes and molecular functions related to lipid metabolism. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that DEGs were enriched in steroid biosynthesis, cholesterol metabolism, non-alcoholic fatty liver disease and other lipid metabolism-related pathways. In addition, gene set enrichment analysis (GSEA) showed that genes were enriched in important pathways affecting lipid metabolism, such as fatty acid elongation and peroxisome proliferator-activated receptor signaling pathway. The results suggested that mild hepatic steatosis affected the lipid metabolic process of dairy cows, and then affected the metabolism of whole body of dairy cows, resulting in differences in production performance of dairy cows such as milk fat content.