Effect of wheat bran on apparent total tract digestibility, growth performance, fecal microbiota and their metabolites in growing pigs

The objective of this study was to evaluate the effects of wheat bran (WB) levels on the apparent total tract digestibility (ATTD) of dietary nutrient in growing pigs, and to test the hypothesis that dietary fiber could alter microbiota community and increase the synthesis of short-chain fatty acid (SCFAs), thus improving the growth performance of nursery pigs. In Exp. 1, 30 barrows with initial body weight (BW) of 40.5 +/- 3.0 kg were allotted to 5 treatments in a completely randomized design. The five treatment diets included 1 control diet and 4 test diets with the WB inclusion level of 5, 15, 25 and 35%, respectively. The concentration of DE and ATTD of nutrients in diets decreased linearly (P < 0.05) as the inclusion level of WB increased. In Exp. 2, 72 nursery pigs with initial BW of 7.12 +/- 1.6 kg were assigned into 2 treatments with 6 replicated pens per treatment in a completely randomized design. The two treatment diets included a control (CON) diet and a test diet with WB inclusion level of 5%. The test diet had no influence on the average daily feed intake (ADFI), average daily gain (ADG) and diarrhea incidence of pigs, but WB supplementary significant decreased (P < 0.05) F/G in the first 2 weeks and over the whole period of 28 days. Moreover, the concentration of butyrate (P < 0.05) and valerate (P < 0.10) in fecal samples of WB supplementation group were greater than those in CON group. Fresh feces were collected and analyzed for microbiota community by 16s RNA sequencing. At the phylum level, the relative abundance of Fibrobacteres in WB supplementation group showed an increased tendency (P < 0.10) compared to,CON group. At the family level, the relative abundance of Prevotellaceae in WB supplementation group showed a decreased tendency (P < 0.10) compared to CON group. Based on Heatmap, the relative abundance of Ruminococcus_1, Ruminococcaceae_UCG-002 and Unclassified-f-Lachnospiraceae genera in WB supplementation group showed an increased tendency compared to CON group. Using the linear discriminant analysis (LDA) effect size (LEfSe) algorithm, relative abundances of Ruminococcaceae, norank_f_ Ruminococcaceae, Ruminococcaceae-NK4A214_group, Veillonella and Prevotellaceae decreased when pigs were fed the WB diet. In conclusion, increasing dietary WB levels had a negative impact on nutrient digestibility in growing pigs. However, 5% dietary WB supplementation altered microbiota community, increased the production of bacterial metabolites, and improved the growth performance in nursery pigs.