Dietary L-arginine levels affect the liver protein turnover and alter the expression of genes related to protein synthesis and proteolysis of laying hens.

Amino acids are considered to be anabolic factors that affect protein turnover. The aim of this study was to test the effects of dietary L-arginine (Arg) levels on protein metabolism in the liver of laying hens and the expression of genes related to protein synthesis and proteolysis. Xinyang black commercial laying hens (n = 864, 31 wk of age) were randomly allotted to 6 treatments with 4 replicates of 36 birds. The dietary treatments were corn-corn gluten meal based diets containing 0.64, 0.86, 1.03, 1.27, 1.42, and 1.66% L-Arg, respectively. Serum concentrations of total protein and albumin were maximized in the 1.27% L-Arg group, and serum concentration of urea acid was the lowest in the 1.27% L-Arg group. The 1.27% L-Arg group had the highest fractional protein synthesis rate and fractional protein gain rate in the liver. Consistent with the data on protein turnover, mRNA abundances of target of rapamycin (TOR) and ribosomal protein S6 kinase 1 increased in the liver of layers fed 1.27% L-Arg, while mRNA abundances of cathepsin B and 20S proteasome decreased at the same dietary L-Arg level. In conclusion, the dietary level of L-Arg increased the liver fractional protein synthesis rate and fractional protein gain rate of laying hens, and the action of an appropriate level of dietary L-Arg involves upregulating the gene expression of the TOR signaling pathway accompanied by suppressing the mRNA expression of cathepsin B and 20S proteasome in the liver.