Effects of sodium butyrate and poly-β-hydroxybutyrate on the intestinal resistance and recovery from ammonia nitrogen stress in grass carp (Ctenopharyngodon idella)

To study the effects of dietary butyrate supplementation on the resistance and recovery from ammonia nitrogen stress in the intestine, grass carp ( Ctenopharyngodon idella ) were administered four distinct diets for 56 days: control diet (CK group), 600 mg butyrate /kg powdered sodium butyrate (PSB group), microencapsulated sodium butyrate (MSB group) and poly-β-hydroxybutyrate (PHB group). After feeding, the fish were exposed to ammonia nitrogen (10.47 ± 0.67 mg/L) for 96 hours, followed by a 15- day recovery in pristine water. Our results revealed that dietary PSB, MSB and PHB primarily increased intestinal crypt depth and goblet cell count, and PHB also elevated the ratio of villus area to intestinal area. Moreover, three additions significantly increased the levels of acid phosphatase (ACP), lysozyme (LZM), total superoxide dismutase (T-SOD), total antioxidant capacity (T-AOC) and β defensin (β-DF) of the intestine. Meanwhile, these supplements significantly decreased the intestinal contents of interleukin-1β (IL-1β) and malondialdehyde (MDA). In acute ammonia nitrogen stress and recovery experiment, the addition of PSB, MSB and PHB decreased lipid peroxides (MDA) and enhanced antioxidant capacity (T-SOD and T-AOC), thereby effectively mitigating ammonia-induced oxidative stress. These additives further enhanced intestinal non-specific immunity, as evidenced by the increased levels of ACP, LZM and β-DF, and simultaneously alleviated inflammatory response (IL-1β) induced by ammonia nitrogen. Furthermore, the integrated biomarker response analysis revealed that MSB group exhibited a superior effect. In conclusion, dietary supplementation of 600 mg/kg butyrate demonstrated an enhanced ability to mitigated ammonia nitrogen stress and recovery in the intestine of grass carp.