Safflower Promotes the Immune Functions of the Common Carp (Cyprinus carpio L.) by Producing the Short-Chain Fatty Acids and Regulating the Intestinal Microflora

Abstract

To evaluate the functions of safflower on aquatic animal, the effects of dietary safflower supplementation on growth performance, immunity response, short-chain fatty acids, and intestinal microflora of common carp (Cyprinus carpio L.) were studied in the present study. Four isonitrogen and isolipid experimental diets were formulated by adding 0, 0.25%, 0.50%, and 1.00% safflower to the basal diet (CON, S-0.25%, S-0.50%, and S-1.00%, respectively). The results showed that safflower supplementation (S-0.50%) significantly improves the growth performance (FBW, WGR, SGR) compared with that of the CON group ( $P<0.05$ ). Similarly, safflower also promoted the CAT and LZM activities in the midgut, yet the content of MDA in the S-0.50% group was reduced ( $P<0.05$ ). The content of proinflammatory factors (IL-1β, IL-12) in serum underwent significant reduction ( $P<0.05$ ); the level of anti-inflammatory factor IL-10 had an upward trend in the S-0.50% group. Moreover, the mRNA expression levels of the IL-10, TGF-β, NF-κB, and TLR-1 gene in the head kidney were remarkably upregulated ( $P<0.05$ ) in safflower addition groups, while IL-6 and IL-1β were downregulated significantly in the S-1.00% group ( $P<0.05$ ). After 96 hours of the A. hydrophila challenge test, the survival rate of common carp had been improved greatly with the safflower addition, which was most impressive in the S-1.00% group. Additionally, the levels of acetic acid and butyric acid in intestinal contents were significantly higher in the S-0.50% and S-1.00% groups than in the CON group ( $P<0.05$ ). Dietary safflower increased the intestinal microbiota abundance of Fusobacteria at the phylum level. At the genus level, the abundance of beneficial bacteria (Lactobacillus and Bifidobacterium) increased significantly in the S-1.00% group; some pathogens such as Aeromonas, Shigella, and Streptococcus were inhibited. Spearman coefficient analysis revealed that the contents of SCFAs were positively correlated with probiotics and negatively correlated with pathogens. In summary, safflower addition at an appropriate dose can promote the immune functions of the common carp by producing the short-chain fatty acids and regulating the intestinal microflora.