Abstract: 【Objective】 This study aimed to investigate the effects of dietary net energy levels on colonic microbiota composition and short-chain fatty acid profiles in Tunchang pigs. 【Method】 Forty healthy Tunchang pigs,with an average body weight of 10.00 kg±0.86 kg and similar body condition,were randomly divided into four dietary treatment groups (JC1,JC2,JC3,and JC4),with 5 replicates per group and 2 pigs per replicate.The four treatment groups were provided experimental diets with net energy levels of 10.65,10.15,9.65,and 9.15 MJ/kg,respectively.The experiment was terminated when the pigs reached an average body weight of 25.00 kg,with a total experimental period of 42 days.At the end of the trial,one pig was selected from each replicate to collect cecal contents for gut microbiota analysis and short-chain fatty acid composition analysis. 【Result】 ①Compared with JC3 group,the final body weight and average daily gain were significantly lower (P＜0.05),the feed-to-gain ratio was significant higher (P＜0.05) of Tunchang pigs in JC1,JC2 and JC4 groups.②Analysis of the diversity of intestinal flora showed that there were significant differences in both alpha diversity and beta diversity among the groups treated with different net energy levels of rations (P＜0.05).At the phylum level of colonic microbiota composition,the relative abundance of Spirochaetes was significantly lower in JC1,JC3 and JC4 groups compared with JC2 group (P＜0.05),while the relative abundance of Actinobacteria was significantly lower in JC2 and JC3 groups compared with JC4 group (P＜0.05).At the genus level,the relative abundance of Roseburia and Coprococcus was significantly lower in JC1,JC2 and JC4 groups compared with JC3 group (P＜0.05),and the relative abundance of Ruminococcus was also significantly lower in JC1 and JC2 groups compared with JC3 group (P＜0.05).In addition,the relative abundance of Treponema in JC2 group was significantly higher than that in the other three groups (P＜0.05).③Metabolomic analysis of short-chain fatty acids in colon contents showed that the content of caproic acid was significantly higher in JC2 group than that in JC3 group (P＜0.05),and extremely significantly higher than JC4 group (P＜0.01).And butyric acid content had a tendency to be elevated in JC3 group compared with JC1,JC2 and JC4 groups (0.05＜P＜0.10). 【Conclusion】 Compared to the recommended net energy level of 10.15 MJ/kg (JC2), reducing the dietary net energy level to 9.65 MJ/kg could improve the composition of short-chain fatty acids by increasing the richness of the intestinal microbiota and the relative abundance of beneficial bacteria,thereby promoting the growth performance of Tunchang pigs.

Key words: net energy; Tunchang pig; colonic microbiota; short-chain fatty acids