【Objective】 Feed Conversion Rate (FCR) is an important economic trait index in livestock and poultry production. Through the analysis of intestinal flora and small molecular metabolites, the factors affecting the regulation of FCR in broilers were explored. 【Method】 Good health condition, the same batch of 0-day-old Jatropha curcas chicks were selected, free to feed and drink. At 57 days of age, 500 males with normal development and similar body weight ((2 374.96 ± 214.39) g) were selected and transferred to the assay house, with an acclimatization period of 3 days. The official assay was performed at 60 days of age, with an experimental period of 18 days, and 20 birds with high feed conversion rate (HF) and low feed conversion rate (LF) were selected for slaughtering at the marketable age (78 days of age), respectively, based on the results of the automated feeding system. Twenty birds with HF and LF were selected for slaughter at the market age (78 days old) according to the results of the automatic feeding system. Chicken intestines were isolated for determination of intestinal morphology, while cecal chow was harvested for joint analysis of microbial and small molecule metabolite differences between the HF and LF cecums of broiler chickens and correlation analyses using 16S rRNA sequencing and globally precise non-targeted metabolomics. 【Result】 (1) Compared with the LF group, the daily weight gain in HF group was significantly decreased (P<0.05), while the FCR was significantly increased (P<0.05), the jejunal length was significantly decreased (P<0.05), rectal length was significantly increased(P<0.05), and jejunal villus height/crypt depth ratio was significantly decreased(P<0.05). (2) Compared with the LF group, Chao1, Shannon, Observed_species, and Faith_pd indices were significantly decreased in the HF group (P<0.05). The difference in compositional structure between HF and LF was large (P<0.05). Genera with LDA values greater than 3 in the LF group were Blautia_A, Barnesiella, Massilistercora, Papillibacter, Mitsuokella, Paramuribaculum, and UBA738. The genera with LDA values greater than 3 in the HF group were Desulfovibrio_R, Alloprevotella, and Intestinimonas. (3) Thirty-two differential metabolites were screened, among which Docosahexaenoic acid, beta-carotene, and D-Mannose 6-phosphate were more multiplicative. Among these differential metabolites fatty acyl, benzene and substituted derivatives were more frequent. (4) The microorganisms that showed significant negative correlation with FCR values were Papillibacter, Blautia_A, and Paramuribaculum. The metabolites that showed a significant negative correlation with FCR values were Phenylethylamine, beta-Carotene, Antibiotic JI-20A, trans-Cinnamate, Xanthosine, 3-Methoxyanthranilate, Phthalic acid, Niacinamide, gamma-L-Glutamyl-D-alanine, 5-Nitro-2-(3-phenylpropylamino) benzoic acid, Desaminotyrosine, and 1-palmitoylglycerophosphocholine. The metabolites that showed significant positive correlation with FCR values were Phosphorylcholine. Gamma-L-Glutamyl-D-alanine was significantly positively correlated with Blautia_A, while Phosphorylcholine was significantly positively correlated with Intestinimonas. 【Conclusion】 The broiler feed conversion was associated with intestinal flora and metabolites, while Papillibacter, Blautia_A, Barnesella, and Mitsuokella might be marker microorganisms affecting feed efficiency. Desmethyltyrosine, β-carotene, Xanthosine, gamma-L-Glutamyl-D-alanine, and Phosphorylcholine might be marker metabolites affecting feed efficiency. Intestinal flora could influence FCR directly or through microbial metabolites, and microbe-metabolite associations suggested specific pathways of action that may influence feed conversion.
