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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.

In order to explore the effect of dietary supplementation of Clostridium butyricum on the volatile flavor substances in the meat of small-tailed Han sheep during postmortem aging and its possible mechanism, the Longissimus dorsi muscle of small-tailed Han sheep slaughtered at the age of six months was taken for postmortem maturation at 4 ℃, and then the volatile flavor substances, the contents of lipid metabolism-related enzymes including adenosine monophosphate activated protein kinase (AMPK), acetyl CoA carboxylase (ACC) and carnitine lipoyltransferase 1 (CPT1) were measured on days 0, 1, 2, 3, 4 and 5. The results of electronic nose test showed that the contents of alkanes, hydroperoxide and nitrogen oxides in the C. butyricum supplementation group were higher than in the control group without C. butyricum supplementation. According to the results of gas chromatography-mass spectrometry (GC-MS), the types of aldehydes, alcohols and ketones in the C. butyricum group were more than in the control group, while the contents of fatty oxidation products such as octanal, nonanal, decanal and heptaldehyde were obviously reduced. The key flavor substances common to both groups, as determined by relative odor activity value (ROAV), included octanal, nonanal, trans-2-decenal and 1-octen-3-ol, nonanal being the greatest contributor to the flavor of lamb meat. Compared with the control group, the contents of AMPK and CPT1 in the C. butyricum group decreased significantly during postmortem aging (P < 0.05), while the contents of ACC in the C. butyricum group were significantly higher than those in the control group at 0, 1, 3 and 5 days postmortem (P < 0.05). The correlation analysis showed that AMPK and CPT1 were significantly positively correlated with nonanal (P < 0.001), while ACC was significantly negatively correlated with nonanal and decanal (P < 0.001). In conclusion, the addition of C. butyricum to the diet can affect the volatile flavor substances in the meat of small-tailed Han sheep during postmortem aging by regulating the AMPK-ACC-CPT1 signaling pathway.