Dietary tributyrin supplementation promotes the growth by improving intestinal digestive and antioxidant capacity and the abundance of intestinal beneficial bacteria for swimming crab (Portunus trituberculatus)

This study aimed to evaluate the effects of tributyrin (TB) supplementation on the growth, digestive enzyme activity, lipid metabolism, and intestinal health of swimming crab (Portunus trituberculatus) with an initial weight of 12.50 ± 0.02 g. Six experimental diets were formulated, which containing 0%, 0.025%, 0.05%, 0.10%, 0.20%, and 0.40% of TB, respectively. Results showed that crabs fed the diet containing 0.10% TB had significantly higher values of percent weight gain (PWG) and specific growth rate (SGR) than those in other treatments. Crabs fed the diet without TB supplementation showed dramatically higher contents of T-CHO, TG, and MDA in serum than those in other treatments, opposite patterns were recorded for the activities of T-SOD, PPO, NO, ACP, and AKP. The activities of antioxidant enzyme including T-AOC, T-SOD, ACP, AKP and GSH-Px in hepatopancreas were significantly affected by dietary TB levels. Meanwhile, crabs fed the diet without TB supplementation had significantly lower activities of trypsin, lipase, and amylase in the intestine than those in other treatments. The relative expression levels of genes related to antioxidant capacity in the hepatopancreas and intestine were markedly decreased when crabs fed the diet without TB supplementation; however, crabs fed the diet without TB supplementation exhibited the highest expression of genes linked to inflammation among treatments, and the expression levels of crustin and lyso in the intestine were significantly affected by dietary TB levels. The expression levels of genes related to energy metabolism and intestinal immune barrier in the intestine were also influenced by dietary TB levels. Dietary TB supplementation could reduce lipid accumulation in hepatopancreas by upregulating lipid catabolism related genes expression levels and decreasing lipid anabolism related gene expression levels. Muscularis thickness, fold width, and fold height in the intestine were significantly increased with dietary TB increasing from 0% to 0.10%; moreover, lipid droplets, the diameter of R cells and the area of R cells in the hepatopancreas significantly decreased with an increase of dietary TB levels. Additionally, the number of Actinobacteria and Bacteroides significantly increased with an increase of dietary TB levels. To sum up, the TB requirement of swimming crab was 0.089% based on two slope broken-line analysis of PWG. The findings of the current study indicate that TB is an effective growth promoter that can serve as a nutritional supplement to improve the growth performance, promote health and regulate lipid metabolism of swimming crab.