Dietary propionate administration improves growth performance, hepatic lipid deposition, and intestinal activity of digestive enzymes, inflammation, bacterial population, and antioxidant capacity in rainbow trout, Oncorhynchus mykiss.

The present study aimed to investigate the effects of dietary sodium propionate on growth performance, hepatic lipid deposition, and intestinal activity of digestive enzymes, inflammation, bacterial population, and antioxidant capacity in rainbow trout, Oncorhynchus mykiss. The fish were fed diets supplemented with 0 g/kg (CTL), 1 g/kg (P1), 2.5 g/kg (P2.5), or 5 g/kg (P5) sodium propionate for 70 days. The results showed significant (P < 0.05) linear or quadratic relationships between dietary sodium propionate levels and all tested parameters. Growth performance and feed efficiency significantly increased in the P1 and P2.5 treatments, but decreased in the P5 treatment, compared to the CTL group. Hepatosomatic index significantly decreased in the P1 and P2.5 treatments, but increased in the P5 treatment, compared to the CTL group. The P1 and P2.5 treatments exhibited significantly lower viscerosomatic indices than the CTL group. The P1 and/or P2.5 treatments exhibited significantly higher intestinal amylase, lipase, trypsin, chymotrypsin, superoxide dismutase (SOD), catalase (CAT), and lower intestinal malondialdehyde (MDA), plasma glucose, and triglyceride levels than the CTL treatment. On the other hand, the P5 treatment exhibited significant decrease in intestinal lipase, SOD, CAT, and higher intestinal MDA, plasma glucose, cortisol, triglyceride, and cholesterol levels than the CTL group. The intestinal total viable bacteria significantly decreased in the propionate treatments, and the lowest level was observed in the P2.5 treatment. The P1 and P2.5 treatments had significantly higher intestinal abundance of Lactobacillus sp. and lower Aeromonas hydrophila, Yersinia ruckeri, and Streptococcus iniae than the CTL group. The pathogenic bacteria showed significant elevations in the P5 treatment, compared to the CTL group. The propionate treatment groups showed significant up-regulations in intestinal heat shock protein 70 expression than the CTL group. The intestinal expression of tumor necrosis factor-alpha and interleukin-1 beta significantly decreased in the P1 and P2.5 treatments, while increased in the P5 treatment, compared to the CTL group. The intestinal expression of defensin significantly increased in the P1 and P2.5 treatments, while decreased in the P5 treatment, compared to the CTL group. In conclusion, dietary sodium propionate can improve the growth and intestinal health of rainbow trout. Based on the results, 2.5 g/kg sodium propionate is suitable for rainbow trout, but higher levels induce growth retardation, hepatic lipid accumulation, and intestinal oxidative stress, inflammation, and dysbiosis.