Growth performance of post-weaned Holstein male calves accelerated by branched-chain volatile fatty acids addition with up-regulated hepatic mTOR expression via insulin and insulin-like growth factor-1 (IGF-1) signalling pathway

The study evaluated the effects of branched-chain volatile fatty acids (BCVFA) addition on growth performance, ruminal fermentation, nutrient digestibility, hormone secretion and hepatic gene expression in dairy calves. Thirty-six Holstein male calves (45 ± 3.5 days of age; 56 ± 1.8 kg body weight) were randomly assigned to four groups: control, low-BCVFA (LBC), mediumBCVFA (MBC) and high-BCVFA (HBC) with 0, 1.5, 3.0 and 4.5 g BCVFA per kg dietary dry matter (DM), respectively. Supplemental BCVFA was premixed into concentrate of the ration. DM intake and average daily gain (ADG) were increased, and feed conversion ratio was decreased in MBC and HBC groups in comparison to control one. In MBC and HBC groups ruminal pH and ammoniaN were lower, whereas total volatile fatty acids concentration was higher than in control group. Acetate:propionate ratio and digestibility of DM, organic matter, crude protein, ether extract, neutral detergent fibre and acid detergent fibre were higher in MBC and HBC groups than in control one. Blood concentration of glucose, albumin, growth hormone releasing hormone, growth hormone (GH), insulin (INS) and insulin-like growth factor-1 (IGF-1), and hepatic mRNA abundance of GH, INS, IGF-1, receptors of GH, INS and IGF-1, mammalian target of rapamycin (mTOR), eukaryotic translation initiation factor 4E-binding protein 1 and ribosomal protein S6 kinase were higher in MBC and HBC than in control group. It was indicated that BCVFA addition increased ADG by stimulating feed intake, ruminal fermentation, nutrient digestion and hepatic mTOR expression, and the optimum dose of BCVFA was 3.0 g/kg DM under the current experimental conditions.