Effects of dietary acidifier on growth, antioxidant capacity and intestinal health of Micropterus salmoides

In order to explore the effects of dietary acidifiers on the growth, antioxidant indices and intestinal health of Micropterus salmoides, five isonitrogenous and isolipid diets containing different levels of acidifiers (0%, 0.05%, 0.10%, 0.15% and 0.20%) were fed to M. salmoides with an initial body weight of (21.31±0.18) g for 64 days. The results showed that the weight gain rate and specific growth rate of largemouth bass increased first and then decreased with the increase of dietary acidifier level, and reached the maximum value in the 0.15% group. Compared with the control group, supplementing 0.10%-0.15% of dietary acidifiers significantly decreased feed conversion ratio, and significantly increased whole-body crude lipid content and protein deposition rate. The apparent digestibility of dry matter and gross energy of M. salmoides were significantly increased by dietary acidifiers (P<0.05). The intestinal lipase activity of M. salmoides was significantly higher than that of the control group after 0.15% of dietary acidifier (P<0.05). Compared with the control group, the triglyceride content and the total cholesterol content in the 0.15% group were significantly increased, and the high-density lipoprotein cholesterol content in the 0.15% group was significantly increased (P<0.05). Serum total antioxidant capacity, intestinal total antioxidant capacity and superoxide dismutase activity of M. salmoides were significantly increased (P<0.05), and serum aspartate aminotransferase activity and liver malondialdehyde content were significantly decreased by addition of 0.10%-0.15% of dietary acidifier (P<0.05). The villus length, villus width and muscularis thickness in 0.15% group were significantly higher than those in the control group (P<0.05). Compared with the control group, supplementation of 0.15% of dietary acidifiers significantly up-regulated the mRNA expression levels of antioxidant related genes (nrf2, cat and sod1) (P<0.05), and significantly down-regulated the mRNA expression level of anti-inflammatory factor (il-10) gene (P<0.05). Supplementation of 0.20% of dietary acidifier significantly down-regulated the mRNA expression levels of pro-inflammatory factors (tnf-α and il-1β) genes (P<0.05). The results of the broken line model based on the weight gain rate and feed conversion ratio showed that the appropriate supplemental amount of acidifier in the diet of M. salmoides was 0.148%-0.152%. In conclusion, supplementation with 0.15% dietary acidifier could promote the growth and antioxidant capacity of M. salmoides, reduce intestinal inflammation level and maintain intestinal health.