Effects of Chinese yam peels on immunity and gut microbiota in cyclophosphamide-induced chickens and optimization of extraction process

Yam is famous for its nutritional and medicinal values and is widely distributed around the world, among which the Chinese yam (Dioscorea opposita thunb. cv. Tiegun) from Jiaozuo City, Henan Province is the most prominent. Chinese yam peel (CYP) is a waste product after processing, but it still retains abundant pharmacological compounds. In this study, the extraction process of CYP water extracts was optimized by single factor and response surface method according to the extraction rate and polysaccharide content of CYP extracts. The results showed that the optimal extraction process of CYP was solid-liquid ratio of 1:24, the extraction temperature of 75℃, and the extraction time of 4.4 h. The extraction rate of CYP extracts was 19.46 %, and the polysaccharide content was 100.53 mg/kg obtained by this extraction process. Seven-day-old chickens were given intramuscular injection of cyclophosphamide (CTX) for 3 days to establish immunosuppression models, supplemented with 0.5g/kg, 1g/kg and 2g/kg diet, respectively, and immunized with Combined Newcastle Disease and Infectious Bronchitis Live Vaccine. The results showed that different doses of CYP significantly inhibited CTX-induced decrease in body weight, thymus index, spleen index and bursa of Fabricius index. The levels of immunoglobulin IgG, IgM and Newcastle disease antibody in serum of chicken were also significantly reversed by CYP. Yam peel also repaired the intestinal barrier by up-regulating the relative mRNA expression of ZO-1, Claudin-1 and Occludin in jejunal, and increasing the ratio of villus height and crypt depth. In addition, CYP significantly improved the composition, richness and diversity of jejunal microbiota, and enriched the KEGG metabolic pathways related to amino acids, including histidine metabolism, cysteine and methionine metabolism, alanine, aspartate and glutamate metabolism. CYP also upregulated the abundance of beneficial bacteria Faecalibacterium, Subdoligranulum, and lachnospira, which were stronger positively correlated with the improvement effects of CTX-induced broiler, and downregulated the abundance of harmful bacteria Pseudomonas. The protective effect of CYP on CTX-induced broilers may be due to the regulation of gut microbiota by CYP, which in turn enhances immune function and repairs intestinal barrier.