Dietary choline can partially spare methionine to improve the feeds utilization and immune response in juvenile largemouth bass (Micropterus salmoides): Based on phenotypic response to gene expression

Abstract

Present study was conducted to explore the interrelationship between dietary methionine and choline in feed formulations for largemouth bass (Micropterus salmoides). Four isonitrogenous (51.0%) and isolipidic (14.0%) diets were formulated supplemented or not supplemented with methionine and choline: NC diet (basic diet), Met diet (basic diet supplemented with methionine), Cho diet (basic diet supplemented with choline) and PC diet (basic diet supplemented with methionine and choline). Fish with an initial body weight of 8.01 ± 0.08 g were fed with each diet for 8 weeks. Significant interactions were found between dietary methionine and choline on growth performance, plasma nutrient concentration, genes expression level of nutrient sensing signaling pathways, nutrient metabolism and immune response. Dietary methionine addition had great effects on improving weight gain rate (WGR), specific growth rate (SGR) and Feed efficiency ratio (FER), while choline supplementation only increased FER (P＜0.05). Both added methionine and choline had higher WGR, SGR and FER than the other groups (P＜0.05). Moreover, compared with NC group, PC, Met and Cho groups also activated growth hormone/insulin-like growth factor (GH-IGF), mammalian target of rapamycin (mTOR) pathway and shut down amino acid response (AAR) pathway to further enhanced glucose, lipid synthesis (P＜0.05). Dietary choline and methionine were similar in regulating the activity of signaling pathways (P > 0.05). Supplemented both together had the most significant effect on promoting nutrient accumulation and improving feed efficiency (P＜0.05). Furthermore, methionine and choline addition also enhanced the gene expression level of key regulators in immune response. Combined supplementation could improve this effect than the individual supplementation to a certain degree. Therefore, when methionine met the requirement of largemouth bass, choline supplementation could further raise the utilization of methionine and partially spare methionine efficiently. This study provided a more reasonably method for using choline to improve growth and feed utilization which could maximize growth and avoid the toxic effect of excessive methionine addition in diets.