Dimethyl-β-propiothetine (DMPT) supplementation under the all-plant protein diet enhances growth performance, digestive capacity and intestinal structural integrity for on-growing grass carp (Ctenopharyngodon idella)

Abstract

This study aimed to investigate the effects of dimethyl-β-propiothetine (DMPT) supplementation under the all-plant protein diet on the growth, digestive capacity, oxidative damage and intestinal structural integrity of on-growing young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp (216 ± 0.29 g) were randomly divided into six groups with three replicates and fed one fish meal (FM) diet and five all-plant protein diets with graded levels of DMPT (0 to 520 mg/kg diet) for 60 days. The results indicated that compared to the FM diet group, the all-plant protein diet without DMPT supplementation (all-plant protein diet group) significantly reduced feed intake (FI), specific growth rate (SGR), percentage weight gain (PWG), and digestive enzyme activities (trypsin, chymotrypsin, lipase and amylase activities) as well as damaged the intestinal histological structure of fish. However, these parameters could be restored to levels equal or superior to the FM diet group at DMPT supplementation levels under the all-plant protein diet up to 260.00 mg/kg diet. This is the first study to show that (1) DMPT supplementation under the all-plant protein diet increased FI and digestive enzyme activities in the intestine were partly related to improved neuropeptide Y content and cholecystokinin content, respectively. (2) DMPT supplementation under the all-plant protein diet enhanced the intestinal structural integrity of fish partially by alleviating oxidative damage and partially by up-regulating antioxidant enzyme activities as well as the mRNA levels of antioxidant enzyme (except CuZnSOD), which were partially related to [Keap1a (not Keap1b)/Nrf2] signalling. (3) Finally, based on the quadratic regression analysis for optimal growth performance indices (FI and PWG) and oxidative damage indices (protein carbonyl and malondialdehyde content), the appropriate levels of DMPT supplementation under the all-plant protein diet for on-growing grass carp were estimated as to be 278.30, 282.78, 326.52 and 299.25 mg/kg diet, respectively. In summary, DMPT supplementation under the all-plant protein diet improved the growth performance and digestive capacity and strengthened the intestinal structural integrity of on-growing grass carp. Simultaneously, it also provided a practical and effective approach to the highly efficient utilisation of plant protein and a reference for the non-fish meal diet formulation of fish.