Effects of dietary protein levels on growth performance, serum indexes, PI3K/AKT/mTOR/S6K signalling and intestinal microbiota of abalone Haliotis discus hannai

A 120-day feeding trial was conducted to assess the effect of dietary protein levels on growth performance, serum indexes, PI3 K/AKT/mTOR/S6 K signalling pathway and intestinal microbiota of abalone Haliotis discus hannai. Abalones (initial body weight: 15.88-16.54 g; initial shell length 41.70-42.40 mm) were fed nine isoenergetic (similar to 16.08 kJ/g) and isolipidic (similar to 42.0 g/kg) experimental diets with 93.5, 116.9, 151.1, 191.8, 230.3, 275.9, 320.3, 360.5 and 405.9 g/kg protein contents, respectively. Results showed that the optimal dietary protein level for H. discus hannai was determined as 259.4 g/kg through second-order polynomial regression analysis for weight gain rate (WGR). Serum TP and urea nitrogen levels were significantly increased when dietary protein levels were higher than 320.3 g/kg (p < .05). The highest gene expressions of phosphatidylinositol 3 kinase (PI3 K), target of rapamycin (mTOR) and ribosomal protein S6 kinase (S6 K) in muscle were found in the treatment with 275.9 g/kg of dietary protein. The excessive dietary protein level (405.9 g/kg) significantly decreased the gene expression of S6 K. Meanwhile, abalone fed with 275.9 g/kg of dietary protein exhibited the highest microbial diversity in intestine as measured by Chao richness and Shannon diversity index. In conclusion, dietary protein level reduced from 259.4 g/kg to 154.0 g/kg or increased from 259.4 to 323.0 g/kg, the WGR of abalone might be depressed with 5% likelihood. Over high (>360.5 g/kg) or low (<151.1 g/kg) dietary protein levels had negative effects on growth performance, serum indexes, PI3 K/AKT/mTOR/S6 K signalling and microbial diversity in intestine of abalone.

Automated summary

This study identified the optimal dietary protein level for abalone growth performance and found potential negative effects of high protein diets on serum indexes, signaling pathways, and intestinal microbial diversity.