Gene expression patterns in Korean native ducks (Anas platyrhynchos) with different apparent metabolisable energy (AME) levels

- Circulating mRNA was quantified for determination of AME.
- In excessive energy, lipid biosynthesis associated genes were upregulated.
- Circulating mRNA can be used as a biomarker for AME determination.

Quantitative energy changes in the feeding regimens affect metabolic efficiency and product quality of an animal. Apparent metabolisable energy (AME) is used to evaluate energy utilization such as the difference between the energy consumed and the energy lost. Given the importance of the diet in the profitability we focused on determination of AME levels using biomarkers based on molecular techniques. qRT-PCR was performed to determine gene expression differences in ducklings with different metabolisable energy (ME) levels and potential biomarker genes from circulating mRNA in the body fluid based on estimated AME values. Muscle tissues and cell-free plasma samples were obtained from ducklings fed at three different ME levels (basal ME: 2300; AME: 2900; high ME: 3300 kcal/kg diet). We first identified that 18 S ribosomal RNA was the most suitable endogenous reference gene for determining gene expression analysis. Next, we investigated expression levels of genes related to cell growth, proliferation, oxidative stress, myogenic differentiation, adipocyte differentiation, and mitochondrial function. qRT-PCR assay demonstrated that MAPK8, MAP2K4, HADHA, CSRP3, and MYL1 were gradually up-regulated at the AME and high ME levels. However, PRKAG2, CRH, and PPARG transcript levels were significantly increased in the muscle and the cell-free plasma at the excessive high ME level but not at the AME and the basal ME level. Finally, HSP90AA1 and HSPB7 were not different between AME and high ME level. Our findings suggest that altered patterns of gene expression in response to different levels of energy are useful biomarkers to evaluate the AME value with growing ducklings. Upregulation of genes including MAPK8, PRKAA2, and PRKAG2 at the excessive high ME and their enrichment for lipid and fatty acid biosynthetic process in gene network analysis also supported our molecular approach using circulating nucleic acid in the body fluid.