Effects of dietary tryptophan on protein metabolism and related gene expression in Yangzhou goslings under different feeding regimens.

This study was conducted to investigate the effects of feeding regimens and dietary Trp levels on protein metabolism and regulation of the related gene expression in Yangzhou goslings. A 2 × 3 factorial completely randomized experiment was applied, and the treatments were designed as 2 feeding regimens (ad libitum vs. restricted feeding), and each contained 3 levels of Trp (low-Trp group, 0.14%; medium-Trp group, 0.22%; high-Trp group, 0.30%). The results show that ADG and feed conversion ratio (FCR) were significantly affected by feeding regimens (P < 0.05); dietary Trp levels influenced ADG and ADFI in the starter and overall period (P < 0.05), and interactions between Trp levels and feeding regimens on ADG, ADFI, and FCR were observed in different growing periods (P < 0.05). Serum total protein, triglycerides, and total cholesterol levels in the ad libitum group were higher than those in the restricted feeding group (P < 0.05), and the concentration of serum total protein, glucose, and insulin-like growth factor-I were higher in the medium-Trp and high-Trp groups (P < 0.05); however, serum uric acid, triglyceride, and cortisol levels were reduced in the high-Trp group (P < 0.05). Feeding regimen and dietary Trp levels affected serum glucose (P < 0.05) interactively. In the ad libitum group, tryptophanyl tRNA synthetase (TTS) mRNA expressed at a higher level in the high-Trp treatment, whereas expression of poultry target of rapamycin (pTOR) and p70 ribosomal protein S6 kinase1 (S6K1) mRNA was upregulated in the low-Trp treatment (P < 0.05). Expression and phosphorylation levels of pTOR were upregulated in thigh tissue with increased dietary Trp, but cathepsin B and 20S protease mRNA expression decreased (P < 0.05). It was concluded that the protein deposition in gosling thigh tissue was affected by dietary Trp through positive regulation of the TTS mRNA and pTOR protein expression and phosphorylation levels for protein synthesis, as well as the suppression of protein degradation-related gene expression.