Fine-Tuning of Postprandial Responses via Feeding Frequency and Leucine Supplementation Affects Dietary Performance in Turbot (Scophthalmus maximus L.)

Background: Feeding-induced cell signaling and metabolic responses affect utilization of dietary nutrients but are rarely taken advantage of to improve animal nutrition. Objectives: We hypothesized that by modulating postprandial kinetics and signaling, improved dietary utilization and growth performance could be achieved in animals. Methods: Juvenile turbot (Scophthalmus maximus L.) with an initial mean +/- SD weight of 10.1 +/- 0.01 g were used. Two feeding frequencies (FFs), either 1 or 3 meals/d at a fixed 2.4% daily body weight ration, and 2 diets that were or were not supplemented with 1% crystalline leucine (Leu), were used in the 10-wk feeding trial. At the end of the trial, a 1-d force-feeding experiment was conducted using the aforementioned FF and experimental diets. Samples were collected for the analysis of postprandial kinetics of aminoacidemia, mechanistic target of rapamycin (mTOR) signaling activities, protein deposition, as well as the mRNA expression levels of key metabolic checkpoints at consecutive time points after feeding. Results: Increased FF and leucine supplementation significantly enhanced fish growth by 7.68% +/- 0.53% (means +/- SD) and 7.89% +/- 1.25%, respectively, and protein retention by 4.01 % +/- 0.59% and 4.44% +/- 1.63%, respectively, in feeding trial experiments. The durations of postprandial aminoacidemia and mTOR activation were extended by increased FE whereas leucine supplementation enhanced mTOR signaling without influencing the postprandial free amino acids kinetics. Increased FF and leucine supplementation enhanced muscle protein deposition 21.6% +/- 6.85% and 22.3% +/- 1.52%, respectively, in a 24-h postfeeding period. Conclusions: We provided comprehensive characterization of the postprandial kinetics of nutrient sensing and metabolic responses under different feeding regimens and leucine supplementation in turbot. Fine-tuning of postprandial kinetics could provide a new direction for better dietary utilization and animal performances in aquaculture.