Abstract: The objective of this study was to investigate the effect of dietary supplementation with Clostridium butyricum on the fatty acid metabolism and meat quality of small-tailed Han sheep. A total of 24 three-month-old small-tailed Han sheep in good body condition and with body mass of (28.85 ± 2.01) kg were selected and randomly divided into two groups: the control group was fed a basal diet (a typical corn-soybean diet), and the Clostridium butyricum group was fed the basal diet supplemented with Clostridium butyricum with a viable count of 5 × 108 CFU/g at a dose of 5 g/d. The feeding period lasted for 90 days. After slaughter, rumen fluid was collected for metagenomic analysis, and Longissimus dorsi muscle was harvested to determine its eating quality, fatty acid composition, and gene expression associated with fatty acid metabolism by gas chromatography (GC) and real-time fluorescent quantitative polymerase chain reaction (qPCR). The results showed that feeding Clostridium butyricum significantly improved the brightness value (L*), redness value (a*), pH24 h, and intramuscular fat content (P < 0.05), and reduced the shear force of lamb meat (P < 0.05). In addition, the relative contents of palmitic acid and stearic acid were significantly lower (P < 0.05) and the relative contents of oleic acid, α-linolenic acid, eicosapentaenoic acid were significantly higher in Longissimus dorsi from the Clostridium butyricum group than the control group (P < 0.05). qPCR results showed that dietary supplementation with Clostridium butyricum significantly increased the gene expression of sterol regulatory element binding protein 1C (SREBP-1C), stearoyl-CoA desaturase (SCD), peroxisome proliferator-activated receptor gamma (PPARγ), and acetyl-CoA carboxylase (ACC) (P < 0.05). Metagenomic analysis showed that dietary supplementation with Clostridium butyricum increased the abundance of Firmicutes, Clostridium, and Fibrobacters (P < 0.05), and significantly decreased the abundance of Proteobacteria, Butyrivibrio, and Parabacteroides in rumen fluid (P < 0.05). Correlation analysis showed that the relative abundance of Ruminobacter, Prevotella, and Lactobacillus were significantly positively correlated with unsaturated fatty acids relative contents (P < 0.05). In conclusion, the addition of Clostridium butyricum to the diet can change the microbial composition of the rumen, leading to an increase in the gene expression of SREBP-1C, SCD, PPARγ, and ACC to promote fatty acid deposition, and finally improving the eating quality and nutritional value of small-tailed Han sheep meat.

Key words: Clostridium butyricum; small-tailed Han sheep; meat quality; fatty acid composition; fatty acid metabolism-related genes; rumen microorganisms