This study examined the rumen microbiota of Brown Hanwoo, Jeju Black, and Brown Hanwoo × Jeju Black cross-bred steers reared under the same dietary and environmental conditions. Nine steers were included in the study, with three animals per genetic type, and all animals were fed the same total mixed ration. Rumen samples were collected using the stomach-tubing method, and total community DNA was extracted using the repeated bead-beating plus column method. The V3–V4 hypervariable region of the 16S rRNA gene was amplified and sequenced on the Illumina MiSeq platform. The composition of the rumen microbiota was analysed using QIIME 2 for sequence processing and MicrobiomeAnalyst for statistical visualisations. Alpha diversity indices revealed no significant differences in microbial richness or evenness between the three groups. In contrast, beta-diversity analysis revealed significantly distinct microbial community structures. Patescibacteria, Monoglobus, Shuttleworthia, and Lachnospiraceae_UCG-004 were more abundant in the Brown Hanwoo steers than in the steers of the other two genetic types. These findings suggest a possible breed effect on the rumen microbiota composition under controlled dietary conditions.

(Submitted 9 December 2025; Accepted 31 March 2026; Published 27 April 2026)