Dietary Curcumin Supplementation Could Improve Muscle Quality, Antioxidant Enzyme Activities and the Gut Microbiota Structure of Pelodiscus sinensis

SIMPLE SUMMARY: Curcumin (CM) is a hydrophobic polyphenolic compound derived from the rhizome of turmeric (Curcuma longa Linn.). It has been proven to have antioxidant, anti-inflammatory, and nutritional metabolic regulatory functions in mammals. Currently, little is known about its effects on reptiles. In this study, dietary supplementation of 2–4 g/kg curcumin improved the antioxidant enzyme activities and muscle quality of Chinese soft-shelled turtles (Pelodiscus sinensis). Moreover, dietary curcumin supplementation increased the abundance of antioxidant bacteria (Lactobacillus and Flavobacterium) in the gut of turtles and affected hepatic metabolism-related pathways, reducing the crude lipid content of the body. These data could guide curcumin application to promote the health status of turtles. ABSTRACT: This experiment aimed to assess the impact of different dietary curcumin (CM) levels on growth, muscle quality, serum-biochemical parameters, antioxidant-enzyme activities, gut microbiome, and liver transcriptome in Chinese soft-shelled turtles (Pelodiscus sinensis). Five experimental diets were formulated to include graded levels of curcumin at 0 (control, CM0), 0.5 (CM0.5), 1 (CM1), 2 (CM2) and 4 g/kg (CM4). Each diet was randomly distributed to quadruplicate groups of turtles (164.33 ± 5.5 g) for 6 weeks. Our findings indicated that dietary curcumin supplementation did not have a significant influence on growth performance (p > 0.05); however, it significantly improved the muscular texture profiles (p < 0.05). Serum total superoxide dismutase (SOD), liver catalase (CAT), and total antioxidant capacity (T-AOC) activities increased significantly as dietary curcumin levels rose from 0.5 to 4 g/kg (p < 0.05). Dietary curcumin supplementation improved gut microbiota composition, as evidenced by an increase in the proportion of dominant bacteria such as Lactobacillus and Flavobacterium. Liver transcriptome analysis revealed that curcumin altered metabolic pathways in the liver. In conclusion, based on the evaluation of the activities of SOD in serum and CAT in liver under current experimental design, it was determined that the appropriate dietary curcumin supplementation for Chinese soft-shelled turtles is approximately 3.9 g/kg.