Ruminants are a major source of greenhouse gas emissions, and information on ruminant fermentation and microorganisms is essential to understand ruminant digestion, which is associated with environmental pollution. The present study investigated rumen fermentation and microbial diversity according to the three different growth stages of four Hanwoo steers: growing (12 months, G), early fattening (18 months, EF), and late fattening (25 months, LF). No significant differences were observed in rumen pH and ammonia nitrogen among growth stages. Total volatile fatty acids were significantly higher and propionate and valerate significantly lower in G than in EF and LF (p < 0.05). Ten bacterial phyla were detected, including Firmicutes (47.5−53.5%) and Bacteroidetes (28.4−31.7%), which accounted for 79.2−82.3% of the total bacteria. Prevotella accounted for the highest proportion (31.6−42.6%) of all bacteria in this study but did not differ significantly among the different growth stages. Metaprevotella abundance was significantly higher in G than in the other treatments (p < 0.05). In addition, Paraprevotella tended to be higher in LF than in the other treatments (p = 0.056). Given the differences in the genera of microorganisms with relatively low abundance, additional experiments are needed to determine the effect on fermentation.
Keywords: Hanwoo steers; feed composition; growth stages; microbial diversity; rumen fermentation.