The objective of this experiment was to evaluate the effect of different EOC (0.1425% cobalt lactate + 1.13% oregano essential oil + 98.7275% carrier) levels on in vitro rumen fermentation and microbial changes. Six EOC levels (treatments: 0 mg·L−1, CON; 50 mg·L−1, EOC1; 100 mg·L−1, EOC2; 400 mg·L−1, EOC3; 800 mg·L−1, EOC4 and 1500 mg·L−1, EOC5) were selected to be used to in vitro incubation. The in vitro dry matter digestibility (IVDMD), in vitro neutral detergent fiber digestibility (IVNDFD), in vitro acid detergent fiber digestibility (IVNDFD), pH, ammonia-nitrogen (NH3-N) concentration, total volatile fatty acid (TVFA) concentration and microbial protein (MCP) concentration were measured after 48 h incubation, after which the groups with significant nutrient digestibility and fermentation parameters were subjected to 16S rRNA sequencing. The results showed that the total gas production (GP) of the EOC5 group was higher than that of the other groups after 12 h of in vitro incubation. TVFA, NH3-N and MCP concentrations were also shown to be higher in group EOC5 than those in other groups (p < 0.05), while NH3-N and MCP concentrations in the EOC2 group were lower than those in other groups significantly (p < 0.05). The molar ratio of acetic acid decreased while the molar ratio of propionic acid increased after the addition of EOC. 16S rRNA sequencing revealed that the rumen microbiota was altered in response to adding EOC, especially for the EOC5 treatment, with firmicutes shown to be the most abundant (43.1%). The relative abundance of Rikenellaceae_RC9_gut_group was significantly lower, while the relative abundance of uncultured_bacterium_f_Muribaculaceae and Succiniclasticum was significantly higher in the EOC5 group than those in other groups (p < 0.05). Comprehensive analysis showed that EOC (1500 mg·L−1) could significantly increase gas production, alter sheep rumen fermentation parameters and microbiota composition.

The beef quality significantly varies between breeds. Pingliang Red Cattle resembles Wagyu in fat deposition and flavor. To screen key factors affecting beef quality, we performed meat quality trait testing, RNA-seq, and metabolomics on the longissimus dorsi of Pingliang Red Cattle, Wagyu cross F1 generation, and Simmental cattle. The gene and metabolite expression profiles were similar between Pingliang Red Cattle and Wagyu cross F1 generation. Genes such as FASN, ACACA, PLIN1, and FABP4 were significantly upregulated in the Pingliang Red Cattle and Wagyu cross F1 generation (P < 0.05). Similarly, numerous metabolites, such as 3-iodo-l-tyrosine, arachidonic acid, and cis-aconitate, which may improve the beef quality such as fat deposition and tenderness, were found in higher levels in the Pingliang Red Cattle and Wagyu cross F1 generation. This study revealed differences in the transcriptional and metabolic levels between Pingliang Red Cattle and premium beef breeds, suggesting that Pingliang Red Cattle harbors the genetic potential for breeding high-grade beef cattle.