SCFAs improve disease resistance via modulate gut microbiota, enhance immune response and increase antioxidative capacity in the host

To evaluate the effects of dietary short chain fatty acids (SCFAs) on the intestinal health and innate immunity in crucian carp, a six-week feeding trial was carried out with following treatments: basal diet (BD), basal diet supplementation with 1% sodium acetate (BDSA), basal diet supplementation with 1% sodium propionate (BDSP) and basal diet supplementation with 1% sodium butyrate (BDSB). The results showed dietary BDSA, BDSP and BDSB could protect the host against oxidative stress by improving the activity of certain antioxidative enzymes (T-SOD, GSH-Px and CAT). Additionally, dietary SCFAs could enhance mucosal and humoral immune responses by improving certain innate immune parameters in serum and skin mucus productions (IgM, ACH50 and T-SOD). Furthermore, dietary BDSA and BDSP could up-regulate the expression of immune related genes (TNF-α, TGF-β and IL-8) and tight junction protein genes (occludin and ZO-1). Dietary BDSB could also elevate the expression of IL-8, TGF-β, ZO-1 and Occludin in the midgut. Although dietary differences of SCFAs didn't alter the α-diversity of the intestinal flora, they altered the core microbiota. Finally, the challenge trial showed that dietary basal diet supplementation with SCFAs could protect zebrafish against Aeromonas hydrophila. These results suggest that dietary SCFAs could improve innate immunity, modulate gut microbiota and increase disease resistance in the host, which indicated the potential of SCFAs as immunostimulants in aquaculture.